C#: Fix compiler warning of possible null de-reference.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.CSharp/Entities/Attribute.cs

@@ -91,7 +91,7 @@ private void ExtractArguments(TextWriter trapFile)
                     // The current argument is not named
                     // so the previous ones were also not named
                     // so the child index matches the parameter index.
-                    isParamsParameter = Symbol?.AttributeConstructor?.Parameters[childIndex].IsParams == true;
+                    isParamsParameter = Symbol.AttributeConstructor?.Parameters[childIndex].IsParams == true;
                     argSyntax = ctorArguments[childIndex];
                 }
 

csharp/extractor/Semmle.Extraction.CSharp/Entities/NonGeneratedSourceLocation.cs

@@ -22,7 +22,7 @@ public override void Populate(TextWriter trapFile)
                 Position.Span.Start.Line + 1, Position.Span.Start.Character + 1,
                 Position.Span.End.Line + 1, Position.Span.End.Character);
 
-            var mapped = Symbol!.GetMappedLineSpan();
+            var mapped = Symbol.GetMappedLineSpan();
             if (mapped.HasMappedPath && mapped.IsValid)
             {
                 var mappedLoc = Create(Context, Location.Create(mapped.Path, default, mapped.Span));

csharp/extractor/Semmle.Extraction/Entities/Base/CachedEntity`1.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using Microsoft.CodeAnalysis;
 
@@ -30,6 +31,7 @@ protected CachedEntity(Context context) : base(context)
     /// <typeparam name="TSymbol">The type of the symbol.</typeparam>
     public abstract class CachedEntity<TSymbol> : CachedEntity where TSymbol : notnull
     {
+        [NotNull]
         public TSymbol Symbol { get; }
 
         protected CachedEntity(Context context, TSymbol symbol) : base(context)
@@ -52,7 +54,7 @@ public string DebugContents
 
         public override bool NeedsPopulation { get; }
 
-        public override int GetHashCode() => Symbol is null ? 0 : Symbol.GetHashCode();
+        public override int GetHashCode() => Symbol.GetHashCode();
 
         public override bool Equals(object? obj)
         {