title: Repeated Int32Value in protobuf3 (nullable int array)
body: <p>I have the following protobuf message protocol:</p>
  
  <pre><code>message TestMsg
  {
    int32 int = 1;
    google.protobuf.Int32Value nullable_int = 2;
    repeated google.protobuf.Int32Value nullable_int_array = 3; // Runtime fail
  }
  </code></pre>
  
  <p>protoc compiles it fine and in C# all Int32Values are int?. But it fail in runtime with a null argument not allowed exception. I can understand <code>repeated</code> does not not allow null messages. But <code>Int32Value</code> is a WellKnownType so the compiler could generate a special NullValue type if needed.</p>
  
  <p>Is this a limitation in protobuf (not allowing <code>Int32Value</code> in <code>repeated</code>) or is it a limitation/bug in the C# code generation and supporting libraries?</p>
  
  <p>What are the options to do nullable int arrays in protobuf protocol, except creating your own message and codegen?</p>