Improve some error log messages

src/ejabberd_listener.erl

@@ -606,6 +606,11 @@ validate_module_option(Module, Opt, Val) ->
 			       [Opt, Val]),
 		    error
 	    end;
+	[] ->
+	    ?ERROR_MSG("unknown listen option '~s' for '~s' will be likely "
+		       "ignored because the listening module doesn't have "
+		       "any options", [Opt, Module]),
+	    {ok, Val};
 	KnownOpts when is_list(KnownOpts) ->
 	    ?ERROR_MSG("unknown listen option '~s' for '~s' will be likely "
 		       "ignored, available options are: ~s",

src/gen_mod.erl

@@ -526,11 +526,19 @@ validate_opts(Host, Module, Opts, Validators) when is_list(Opts) ->
 			      end
 		      end;
 		  false ->
-		      ?ERROR_MSG("unknown option '~s' for module '~s' will be"
-				 " likely ignored, available options are: ~s",
-				 [Opt, Module,
-				  misc:join_atoms([K || {K, _} <- Validators],
-						  <<", ">>)]),
+		      case Validators of
+			  [] ->
+			      ?ERROR_MSG("unknown option '~s' for module '~s' "
+					 "will be likely ignored because the "
+					 "module doesn't have any options",
+					 [Opt, Module]);
+			  _ ->
+			      ?ERROR_MSG("unknown option '~s' for module '~s' will be"
+					 " likely ignored, available options are: ~s",
+					 [Opt, Module,
+					  misc:join_atoms([K || {K, _} <- Validators],
+							  <<", ">>)])
+		      end,
 		      [{Opt, Val}]
 	      end;
 	 (_) ->