message: Allow null as valid return values to make strict null checks pass.
diff: @@ -883,7 +883,7 @@ export interface ShowMessageRequestParams {
  * and a set of options actions to the user.
  */
  export namespace ShowMessageRequest {
  - export const type = new RequestType<ShowMessageRequestParams, MessageActionItem, void, void>('window/showMessageRequest');
  + export const type = new RequestType<ShowMessageRequestParams, MessageActionItem | null, void, void>('window/showMessageRequest');
  }
  /**
  @@ -1225,7 +1225,7 @@ export namespace CompletionResolveRequest {
  * type [Hover](#Hover) or a Thenable that resolves to such.
  */
  export namespace HoverRequest {
  - export const type = new RequestType<TextDocumentPositionParams, Hover, void, TextDocumentRegistrationOptions>('textDocument/hover');
  + export const type = new RequestType<TextDocumentPositionParams, Hover | null, void, TextDocumentRegistrationOptions>('textDocument/hover');
  }
  //---- SignatureHelp ----------------------------------
  @@ -1237,7 +1237,7 @@ export interface SignatureHelpRegistrationOptions extends TextDocumentRegistrati
  }
  export namespace SignatureHelpRequest {
  - export const type = new RequestType<TextDocumentPositionParams, SignatureHelp, void, SignatureHelpRegistrationOptions>('textDocument/signatureHelp');
  + export const type = new RequestType<TextDocumentPositionParams, SignatureHelp | null, void, SignatureHelpRegistrationOptions>('textDocument/signatureHelp');
  }
  //---- Goto Definition -------------------------------------
  @@ -1475,7 +1475,7 @@ export interface RenameParams {
  * A request to rename a symbol.
  */
  export namespace RenameRequest {
  - export const type = new RequestType<RenameParams, WorkspaceEdit, void, TextDocumentRegistrationOptions>('textDocument/rename');
  + export const type = new RequestType<RenameParams, WorkspaceEdit | null, void, TextDocumentRegistrationOptions>('textDocument/rename');
  }
  //---- Document Links ----------------------------------------------
  @@ -1534,7 +1534,7 @@ export interface ExecuteCommandRegistrationOptions extends ExecuteCommandOptions
  * a workspace edit which the client will apply to the workspace.
  */
  export namespace ExecuteCommandRequest {
  - export const type = new RequestType<ExecuteCommandParams, any, void, ExecuteCommandRegistrationOptions>('workspace/executeCommand');
  + export const type = new RequestType<ExecuteCommandParams, any | null, void, ExecuteCommandRegistrationOptions>('workspace/executeCommand');
  }
  //---- Apply Edit request ----------------------------------------
  