[ DDS ] Fix issue where forwarding requests with no RPC parameters would return an error
[ DDS ] Fix issue where forwarding requests with no RPC parameters would return an error

Another fix for: https://github.com/dart-lang/sdk/issues/41942

Change-Id: I43bd05db968dab92fef81b04fbe13edc0353c502
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149741
Reviewed-by: Ryan Macnak <d738b7f001baf9789095d7dc549cff6de60b011d@google.com>
Commit-Queue: Ben Konyi <67ffcaedcc3dc3d87dddb9627b72dd41756b31b1@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk