Merge pull request #6759 from ObsidianMinor/csharp/extension-length-checks

Add length checks to ExtensionCollection

Author: jtattermusch

csharp/src/Google.Protobuf/Reflection/ExtensionCollection.cs

@@ -48,14 +48,32 @@ internal ExtensionCollection(FileDescriptor file, Extension[] extensions)
  {
  UnorderedExtensions = DescriptorUtil.ConvertAndMakeReadOnly(
  file.Proto.Extension,
- (extension, i) => new FieldDescriptor(extension, file, null, i, null, extensions?[i]));
+ (extension, i) => {
+ if (extensions?.Length != 0)
+ {
+ return new FieldDescriptor(extension, file, null, i, null, extensions?[i]);
+ }
+ else
+ {
+ return new FieldDescriptor(extension, file, null, i, null, null); // return null if there's no extensions in this array for old code-gen
+ }
+ });
  }
 
  internal ExtensionCollection(MessageDescriptor message, Extension[] extensions)
  {
  UnorderedExtensions = DescriptorUtil.ConvertAndMakeReadOnly(
  message.Proto.Extension,
- (extension, i) => new FieldDescriptor(extension, message.File, message, i, null, extensions?[i]));
+ (extension, i) => {
+ if (extensions?.Length != 0)
+ {
+ return new FieldDescriptor(extension, message.File, message, i, null, extensions?[i]);
+ }
+ else
+ {
+ return new FieldDescriptor(extension, message.File, message, i, null, null);
+ }
+ });
  }
 
  /// <summary>