"Dart: Reanalyze Project" and "Open Diagnostic Server" fail under LSP #3158
Description
The requests generated by the LSP client pass [null] as the params when the type is void:
{"jsonrpc":"2.0","id":28,"method":"dart/diagnosticServer","params":[null]}
{"jsonrpc":"2.0","id":31,"method":"dart/reanalyze","params":[null]}