added null check to destructors

src/string/StringBuilder.c

@@ -1,6 +1,9 @@
 #include "tlibc/string/StringBuilder.h"
 
 void StringBuilder_destroy(StringBuilder* b){
+    if(!b)
+        return;
+
     free(b->buffer.data);
     b->buffer = List_construct_size(NULL, 0, 0);
 }