diff --git a/Directory.Build.props b/Directory.Build.props
index 3e7fe9f..6c371ea 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -1,10 +1,14 @@
 <Project>
   <PropertyGroup>
     <LangVersion>latest</LangVersion>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
   </PropertyGroup>
   <PropertyGroup Condition="'$(TargetFramework)' != 'netstandard2.0' and !$(TargetFramework.StartsWith('netcoreapp2')) and !$(TargetFramework.StartsWith('net4'))">
     <DefineConstants>$(DefineConstants);HAS_ASYNC_ENUMERATOR</DefineConstants>
   </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Nullable" Version="1.3.0" PrivateAssets="All" />
+  </ItemGroup>
   <PropertyGroup Condition="'$(GITHUB_ACTIONS)' == 'true'">
     <ContinuousIntegrationBuild>true</ContinuousIntegrationBuild>
   </PropertyGroup>
diff --git a/src/Ben.Demystifier/Ben.Demystifier.csproj b/src/Ben.Demystifier/Ben.Demystifier.csproj
index 71db297..46781c5 100644
--- a/src/Ben.Demystifier/Ben.Demystifier.csproj
+++ b/src/Ben.Demystifier/Ben.Demystifier.csproj
@@ -12,6 +12,7 @@
     <IncludeSource>true</IncludeSource>
     <DebugType>embedded</DebugType>
 	<PublishRepositoryUrl>true</PublishRepositoryUrl>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <PropertyGroup>
diff --git a/src/Ben.Demystifier/EnhancedStackFrame.cs b/src/Ben.Demystifier/EnhancedStackFrame.cs
index bb48548..96661af 100644
--- a/src/Ben.Demystifier/EnhancedStackFrame.cs
+++ b/src/Ben.Demystifier/EnhancedStackFrame.cs
@@ -7,9 +7,9 @@ namespace System.Diagnostics
 {
     public class EnhancedStackFrame : StackFrame
     {
-        private string _fileName;
-        private int _lineNumber;
-        private int _colNumber;
+        private readonly string? _fileName;
+        private readonly int _lineNumber;
+        private readonly int _colNumber;
 
         public StackFrame StackFrame { get; }
 
@@ -21,7 +21,7 @@ namespace System.Diagnostics
 
         public ResolvedMethod MethodInfo { get; }
 
-        internal EnhancedStackFrame(StackFrame stackFrame, ResolvedMethod methodInfo, string fileName, int lineNumber, int colNumber)
+        internal EnhancedStackFrame(StackFrame stackFrame, ResolvedMethod methodInfo, string? fileName, int lineNumber, int colNumber)
             : base(fileName, lineNumber, colNumber)
         {
             StackFrame = stackFrame;
@@ -32,7 +32,7 @@ namespace System.Diagnostics
             _colNumber = colNumber;
         }
 
-        internal bool IsEquivalent(ResolvedMethod methodInfo, string fileName, int lineNumber, int colNumber)
+        internal bool IsEquivalent(ResolvedMethod methodInfo, string? fileName, int lineNumber, int colNumber)
         {
             return _lineNumber == lineNumber &&
                 _colNumber == colNumber &&
@@ -59,7 +59,7 @@ namespace System.Diagnostics
         ///     This information is typically extracted from the debugging symbols for the executable.
         /// </summary>
         /// <returns>The file name, or null if the file name cannot be determined.</returns>
-        public override string GetFileName() => _fileName;
+        public override string? GetFileName() => _fileName;
 
         /// <summary>
         ///    Gets the offset from the start of the Microsoft intermediate language (MSIL)
diff --git a/src/Ben.Demystifier/EnhancedStackTrace.Frames.cs b/src/Ben.Demystifier/EnhancedStackTrace.Frames.cs
index 8e6c6a7..30ed8b2 100644
--- a/src/Ben.Demystifier/EnhancedStackTrace.Frames.cs
+++ b/src/Ben.Demystifier/EnhancedStackTrace.Frames.cs
@@ -44,8 +44,8 @@ namespace System.Diagnostics
                 return frames;
             }
 
-            EnhancedStackFrame lastFrame = null;
-            PortablePdbReader portablePdbReader = null;
+            EnhancedStackFrame? lastFrame = null;
+            PortablePdbReader? portablePdbReader = null;
             try
             {
                 for (var i = 0; i < stackFrames.Length; i++)
@@ -70,6 +70,12 @@ namespace System.Diagnostics
                         (portablePdbReader ??= new PortablePdbReader()).PopulateStackFrame(frame, method, frame.GetILOffset(), out fileName, out row, out column);
                     }
 
+                    if (method is null)
+                    {
+                        // Method can't be null
+                        continue;
+                    }
+
                     var resolvedMethod = GetMethodDisplayString(method);
                     if (lastFrame?.IsEquivalent(resolvedMethod, fileName, row, column) ?? false)
                     {
@@ -85,11 +91,7 @@ namespace System.Diagnostics
             }
             finally
             {
-                if (portablePdbReader is not null)
-                {
-                    portablePdbReader.Dispose();
-                }
-
+                portablePdbReader?.Dispose();
             }
 
             return frames;
@@ -97,12 +99,6 @@ namespace System.Diagnostics
 
         public static ResolvedMethod GetMethodDisplayString(MethodBase originMethod)
         {
-            // Special case: no method available
-            if (originMethod == null)
-            {
-                return null;
-            }
-
             var method = originMethod;
 
             var methodDisplayInfo = new ResolvedMethod
@@ -174,7 +170,7 @@ namespace System.Diagnostics
                                 if (value is Delegate d)
                                 {
                                     if (ReferenceEquals(d.Method, originMethod) &&
-                                        d.Target.ToString() == originMethod.DeclaringType.ToString())
+                                        d.Target.ToString() == originMethod.DeclaringType?.ToString())
                                     {
                                         methodDisplayInfo.Name = field.Name;
                                         methodDisplayInfo.IsLambda = false;
@@ -208,11 +204,10 @@ namespace System.Diagnostics
                 }
                 else if (mi.ReturnType != null)
                 {
-                    methodDisplayInfo.ReturnParameter = new ResolvedParameter
+                    methodDisplayInfo.ReturnParameter = new ResolvedParameter(mi.ReturnType)
                     {
                         Prefix = "",
                         Name = "",
-                        ResolvedType = mi.ReturnType,
                     };
                 }
             }
@@ -278,7 +273,7 @@ namespace System.Diagnostics
             return false;
         }
 
-        private static bool TryResolveGeneratedName(ref MethodBase method, out Type type, out string methodName, out string subMethodName, out GeneratedNameKind kind, out int? ordinal)
+        private static bool TryResolveGeneratedName(ref MethodBase method, out Type? type, out string methodName, out string? subMethodName, out GeneratedNameKind kind, out int? ordinal)
         {
             kind = GeneratedNameKind.None;
             type = method.DeclaringType;
@@ -364,15 +359,18 @@ namespace System.Diagnostics
             return false;
         }
 
-        private static bool TryResolveSourceMethod(IEnumerable<MethodBase> candidateMethods, GeneratedNameKind kind, string matchHint, ref MethodBase method, ref Type type, out int? ordinal)
+        private static bool TryResolveSourceMethod(IEnumerable<MethodBase> candidateMethods, GeneratedNameKind kind, string? matchHint, ref MethodBase method, ref Type type, out int? ordinal)
         {
             ordinal = null;
             foreach (var candidateMethod in candidateMethods)
             {
-                var methodBody = candidateMethod.GetMethodBody();
+                if (candidateMethod.GetMethodBody() is not { } methodBody)
+                {
+                    continue;
+                }
                 if (kind == GeneratedNameKind.LambdaMethod)
                 {
-                    foreach (var v in EnumerableIList.Create(methodBody?.LocalVariables))
+                    foreach (var v in EnumerableIList.Create(methodBody.LocalVariables))
                     {
                         if (v.LocalType == type)
                         {
@@ -387,14 +385,13 @@ namespace System.Diagnostics
 
                 try
                 {
-                    var rawIL = methodBody?.GetILAsByteArray();
-                    if (rawIL == null) continue;
-                    var reader = new ILReader(rawIL);
+                    var rawIl = methodBody.GetILAsByteArray();
+                    var reader = new ILReader(rawIl);
                     while (reader.Read(candidateMethod))
                     {
                         if (reader.Operand is MethodBase mb)
                         {
-                            if (method == mb || (matchHint != null && method.Name.Contains(matchHint)))
+                            if (method == mb || matchHint != null && method.Name.Contains(matchHint))
                             {
                                 if (kind == GeneratedNameKind.LambdaMethod)
                                 {
@@ -462,7 +459,7 @@ namespace System.Diagnostics
             }
         }
 
-        static string GetMatchHint(GeneratedNameKind kind, MethodBase method)
+        static string? GetMatchHint(GeneratedNameKind kind, MethodBase method)
         {
             var methodName = method.Name;
 
@@ -590,28 +587,25 @@ namespace System.Diagnostics
                 }
             }
 
-            if (parameterType.IsByRef)
+            if (parameterType.IsByRef && parameterType.GetElementType() is {} elementType)
             {
-                parameterType = parameterType.GetElementType();
+                parameterType = elementType;
             }
 
-            return new ResolvedParameter
+            return new ResolvedParameter(parameterType)
             {
                 Prefix = prefix,
                 Name = parameter.Name,
-                ResolvedType = parameterType,
                 IsDynamicType = parameter.IsDefined(typeof(DynamicAttribute), false)
             };
         }
 
         private static ResolvedParameter GetValueTupleParameter(IList<string> tupleNames, string prefix, string name, Type parameterType)
         {
-            return new ValueTupleResolvedParameter
+            return new ValueTupleResolvedParameter(parameterType, tupleNames)
             {
-                TupleNames = tupleNames,
                 Prefix = prefix,
                 Name = name,
-                ResolvedType = parameterType
             };
         }
 
@@ -650,8 +644,6 @@ namespace System.Diagnostics
 
         private static bool ShowInStackTrace(MethodBase method)
         {
-            Debug.Assert(method != null);
-
             // Since .NET 5:
             // https://github.com/dotnet/runtime/blob/7c18d4d6488dab82124d475d1199def01d1d252c/src/libraries/System.Private.CoreLib/src/System/Diagnostics/StackTrace.cs#L348-L361
             if ((method.MethodImplementationFlags & MethodImplAttributes.AggressiveInlining) != 0)
diff --git a/src/Ben.Demystifier/EnhancedStackTrace.cs b/src/Ben.Demystifier/EnhancedStackTrace.cs
index 02c063a..d81a9c0 100644
--- a/src/Ben.Demystifier/EnhancedStackTrace.cs
+++ b/src/Ben.Demystifier/EnhancedStackTrace.cs
@@ -101,12 +101,13 @@ namespace System.Diagnostics
 
                 sb.Append("   at ");
                 frame.MethodInfo.Append(sb);
-
-                var filePath = frame.GetFileName();
-                if (!string.IsNullOrEmpty(filePath))
+                
+                if (frame.GetFileName() is {} fileName
+                    // IsNullOrEmpty alone wasn't enough to disable the null warning
+                    && !string.IsNullOrEmpty(fileName))
                 {
                     sb.Append(" in ");
-                    sb.Append(TryGetFullPath(filePath));
+                    sb.Append(TryGetFullPath(fileName));
 
                 }
 
diff --git a/src/Ben.Demystifier/Enumerable/EnumeratorIList.cs b/src/Ben.Demystifier/Enumerable/EnumeratorIList.cs
index c7bb704..a80ff8b 100644
--- a/src/Ben.Demystifier/Enumerable/EnumeratorIList.cs
+++ b/src/Ben.Demystifier/Enumerable/EnumeratorIList.cs
@@ -24,7 +24,7 @@ namespace System.Collections.Generic.Enumerable
         }
 
         public void Dispose() { }
-        object IEnumerator.Current => Current;
+        object? IEnumerator.Current => Current;
         public void Reset() => _index = -1;
     }
 }
diff --git a/src/Ben.Demystifier/Internal/ILReader.cs b/src/Ben.Demystifier/Internal/ILReader.cs
index af442a4..5222e97 100644
--- a/src/Ben.Demystifier/Internal/ILReader.cs
+++ b/src/Ben.Demystifier/Internal/ILReader.cs
@@ -16,7 +16,7 @@ namespace System.Diagnostics.Internal
 
         public OpCode OpCode { get; private set; }
         public int MetadataToken { get; private set; }
-        public MemberInfo Operand { get; private set; }
+        public MemberInfo? Operand { get; private set; }
 
         public bool Read(MethodBase methodInfo)
         {
@@ -38,7 +38,7 @@ namespace System.Diagnostics.Internal
                 return doubleByteOpCode[ReadByte()];
         }
 
-        MemberInfo ReadOperand(OpCode code, MethodBase methodInfo)
+        MemberInfo? ReadOperand(OpCode code, MethodBase methodInfo)
         {
             MetadataToken = 0;
             int inlineLength;
@@ -46,12 +46,12 @@ namespace System.Diagnostics.Internal
             {
                 case OperandType.InlineMethod:
                     MetadataToken = ReadInt();
-                    Type[] methodArgs = null;
+                    Type[]? methodArgs = null;
                     if (methodInfo.GetType() != typeof(ConstructorInfo) && !methodInfo.GetType().IsSubclassOf(typeof(ConstructorInfo)))
                     {
                         methodArgs = methodInfo.GetGenericArguments();
                     }
-                    Type[] typeArgs = null;
+                    Type[]? typeArgs = null;
                     if (methodInfo.DeclaringType != null)
                     {
                         typeArgs = methodInfo.DeclaringType.GetGenericArguments();
diff --git a/src/Ben.Demystifier/Internal/PortablePdbReader.cs b/src/Ben.Demystifier/Internal/PortablePdbReader.cs
index d92d394..534e4d1 100644
--- a/src/Ben.Demystifier/Internal/PortablePdbReader.cs
+++ b/src/Ben.Demystifier/Internal/PortablePdbReader.cs
@@ -68,13 +68,13 @@ namespace System.Diagnostics.Internal
             }
         }
 
-        private MetadataReader GetMetadataReader(string assemblyPath)
+        private MetadataReader? GetMetadataReader(string assemblyPath)
         {
             if (!_cache.TryGetValue(assemblyPath, out var provider))
             {
                 var pdbPath = GetPdbPath(assemblyPath);
 
-                if (!string.IsNullOrEmpty(pdbPath) && File.Exists(pdbPath) && IsPortable(pdbPath))
+                if (!string.IsNullOrEmpty(pdbPath) && File.Exists(pdbPath) && IsPortable(pdbPath!))
                 {
                     var pdbStream = File.OpenRead(pdbPath);
                     provider = MetadataReaderProvider.FromPortablePdbStream(pdbStream);
@@ -86,7 +86,7 @@ namespace System.Diagnostics.Internal
             return provider?.GetMetadataReader();
         }
 
-        private static string GetPdbPath(string assemblyPath)
+        private static string? GetPdbPath(string assemblyPath)
         {
             if (string.IsNullOrEmpty(assemblyPath))
             {
@@ -97,16 +97,16 @@ namespace System.Diagnostics.Internal
             {
                 var peStream = File.OpenRead(assemblyPath);
 
-                using (var peReader = new PEReader(peStream))
+                using var peReader = new PEReader(peStream);
+                foreach (var entry in peReader.ReadDebugDirectory())
                 {
-                    foreach (var entry in peReader.ReadDebugDirectory())
+                    if (entry.Type == DebugDirectoryEntryType.CodeView)
                     {
-                        if (entry.Type == DebugDirectoryEntryType.CodeView)
-                        {
-                            var codeViewData = peReader.ReadCodeViewDebugDirectoryData(entry);
-                            var peDirectory = Path.GetDirectoryName(assemblyPath);
-                            return Path.Combine(peDirectory, Path.GetFileName(codeViewData.Path));
-                        }
+                        var codeViewData = peReader.ReadCodeViewDebugDirectoryData(entry);
+                        var peDirectory = Path.GetDirectoryName(assemblyPath);
+                        return peDirectory is null 
+                            ? null 
+                            : Path.Combine(peDirectory, Path.GetFileName(codeViewData.Path));
                     }
                 }
             }
@@ -116,13 +116,11 @@ namespace System.Diagnostics.Internal
 
         private static bool IsPortable(string pdbPath)
         {
-            using (var pdbStream = File.OpenRead(pdbPath))
-            {
-                return pdbStream.ReadByte() == 'B' &&
-                    pdbStream.ReadByte() == 'S' &&
-                    pdbStream.ReadByte() == 'J' &&
-                    pdbStream.ReadByte() == 'B';
-            }
+            using var pdbStream = File.OpenRead(pdbPath);
+            return pdbStream.ReadByte() == 'B' &&
+                   pdbStream.ReadByte() == 'S' &&
+                   pdbStream.ReadByte() == 'J' &&
+                   pdbStream.ReadByte() == 'B';
         }
 
         public void Dispose()
diff --git a/src/Ben.Demystifier/Internal/ReflectionHelper.cs b/src/Ben.Demystifier/Internal/ReflectionHelper.cs
index c8467fd..354a84f 100644
--- a/src/Ben.Demystifier/Internal/ReflectionHelper.cs
+++ b/src/Ben.Demystifier/Internal/ReflectionHelper.cs
@@ -12,7 +12,7 @@ namespace System.Diagnostics.Internal
     /// </summary>
     public static class ReflectionHelper
     {
-        private static PropertyInfo tranformerNamesLazyPropertyInfo;
+        private static PropertyInfo? tranformerNamesLazyPropertyInfo;
 
         /// <summary>
         /// Returns true if the <paramref name="type"/> is a value tuple type.
@@ -43,15 +43,15 @@ namespace System.Diagnostics.Internal
         /// To avoid compile-time depencency hell with System.ValueTuple, this method uses reflection 
         /// instead of casting the attribute to a specific type.
         /// </remarks>
-        public static IList<string> GetTransformerNames(this Attribute attribute)
+        public static IList<string>? GetTransformerNames(this Attribute attribute)
         {
             Debug.Assert(attribute.IsTupleElementNameAttribue());
 
             var propertyInfo = GetTransformNamesPropertyInfo(attribute.GetType());
-            return (IList<string>)propertyInfo.GetValue(attribute);
+            return propertyInfo?.GetValue(attribute) as IList<string>;
         }
 
-        private static PropertyInfo GetTransformNamesPropertyInfo(Type attributeType)
+        private static PropertyInfo? GetTransformNamesPropertyInfo(Type attributeType)
         {
             return LazyInitializer.EnsureInitialized(ref tranformerNamesLazyPropertyInfo,
                 () => attributeType.GetProperty("TransformNames", BindingFlags.Instance | BindingFlags.Public));
diff --git a/src/Ben.Demystifier/ResolvedMethod.cs b/src/Ben.Demystifier/ResolvedMethod.cs
index a2d31ec..a674cb5 100644
--- a/src/Ben.Demystifier/ResolvedMethod.cs
+++ b/src/Ben.Demystifier/ResolvedMethod.cs
@@ -9,27 +9,27 @@ namespace System.Diagnostics
 {
     public class ResolvedMethod
     {
-        public MethodBase MethodBase { get; set; }
+        public MethodBase? MethodBase { get; set; }
 
-        public Type DeclaringType { get; set; }
+        public Type? DeclaringType { get; set; }
         
         public bool IsAsync { get; set; }
 
         public bool IsLambda { get; set; }
 
-        public ResolvedParameter ReturnParameter { get; set; }
+        public ResolvedParameter? ReturnParameter { get; set; }
 
-        public string Name { get; set; }
+        public string? Name { get; set; }
 
         public int? Ordinal { get; set; }
 
-        public string GenericArguments { get; set; }
+        public string? GenericArguments { get; set; }
 
-        public Type[] ResolvedGenericArguments { get; set; }
+        public Type[]? ResolvedGenericArguments { get; set; }
 
-        public MethodBase SubMethodBase { get; set; }
+        public MethodBase? SubMethodBase { get; set; }
 
-        public string SubMethod { get; set; }
+        public string? SubMethod { get; set; }
 
         public EnumerableIList<ResolvedParameter> Parameters { get; set; }
 
diff --git a/src/Ben.Demystifier/ResolvedParameter.cs b/src/Ben.Demystifier/ResolvedParameter.cs
index 47c8b48..1457d92 100644
--- a/src/Ben.Demystifier/ResolvedParameter.cs
+++ b/src/Ben.Demystifier/ResolvedParameter.cs
@@ -7,13 +7,15 @@ namespace System.Diagnostics
 {
     public class ResolvedParameter
     {
-        public string Name { get; set; }
+        public string? Name { get; set; }
 
         public Type ResolvedType { get; set; }
 
-        public string Prefix { get; set; }
+        public string? Prefix { get; set; }
         public bool IsDynamicType { get; set; }
 
+        public ResolvedParameter(Type resolvedType) => ResolvedType = resolvedType;
+
         public override string ToString() => Append(new StringBuilder()).ToString();
 
         public StringBuilder Append(StringBuilder sb)
diff --git a/src/Ben.Demystifier/ValueTupleResolvedParameter.cs b/src/Ben.Demystifier/ValueTupleResolvedParameter.cs
index 6750ac9..7dacf13 100644
--- a/src/Ben.Demystifier/ValueTupleResolvedParameter.cs
+++ b/src/Ben.Demystifier/ValueTupleResolvedParameter.cs
@@ -9,25 +9,31 @@ namespace System.Diagnostics
 {
     public class ValueTupleResolvedParameter : ResolvedParameter
     {
-        public IList<string> TupleNames { get; set; }
+        public IList<string> TupleNames { get; }
+
+        public ValueTupleResolvedParameter(Type resolvedType, IList<string> tupleNames) 
+            : base(resolvedType) 
+            => TupleNames = tupleNames;
 
         protected override void AppendTypeName(StringBuilder sb)
         {
-            if (ResolvedType.IsValueTuple())
+            if (ResolvedType is not null)
             {
-                AppendValueTupleParameterName(sb, ResolvedType);
-            }
-            else
-            {
-                // Need to unwrap the first generic argument first.
-                sb.Append(TypeNameHelper.GetTypeNameForGenericType(ResolvedType));
-                sb.Append("<");
-                AppendValueTupleParameterName(sb, ResolvedType.GetGenericArguments()[0]);
-                sb.Append(">");
+                if (ResolvedType.IsValueTuple())
+                {
+                    AppendValueTupleParameterName(sb, ResolvedType);
+                }
+                else
+                {
+                    // Need to unwrap the first generic argument first.
+                    sb.Append(TypeNameHelper.GetTypeNameForGenericType(ResolvedType));
+                    sb.Append("<");
+                    AppendValueTupleParameterName(sb, ResolvedType.GetGenericArguments()[0]);
+                    sb.Append(">");
+                }
             }
         }
 
-
         private void AppendValueTupleParameterName(StringBuilder sb, Type parameterType)
         {
             sb.Append("(");