fix event stream v2 deser (#3340)

Author: lucix-aws

codegen/smithy-aws-go-codegen/src/main/java/software/amazon/smithy/aws/go/codegen/JsonRpcProtocolGenerator.java

@@ -25,6 +25,7 @@
 import java.util.stream.Collectors;
 import software.amazon.smithy.codegen.core.Symbol;
 import software.amazon.smithy.go.codegen.CodegenUtils;
+import software.amazon.smithy.go.codegen.EventStreamGenerator;
 import software.amazon.smithy.go.codegen.GoWriter;
 import software.amazon.smithy.go.codegen.ChainWritable;
 import software.amazon.smithy.go.codegen.Writable;
@@ -364,6 +365,16 @@ protected void generateEventStreamDeserializers(
             var outputShape = model.expectShape(streamInfo.getOperation().getOutput().get());
             var functionName = ProtocolGenerator.getDocumentDeserializerFunctionName(outputShape,
                     context.getService(), context.getProtocolName());
+            if (EventStreamGenerator.isV2EventStream(model, streamInfo.getOperation())) {
+                // all of the initial response members are filtered out in the
+                // generated struct, so basically do nothing
+                AwsEventStreamUtils.generateEventMessageRequestDeserializer(context, outputShape,
+                        (ctx, payloadTarget, operand) -> {
+                            ctx.getWriter().get().write("return v, nil");
+                        });
+                continue;
+            }
+
             AwsEventStreamUtils.generateEventMessageRequestDeserializer(context, outputShape,
                     (ctx, payloadTarget, operand) -> {
                         AwsProtocolUtils.initializeJsonEventMessageDeserializer(ctx, "nil,");