Fixed code issues via automatic dart fix

lib/api/marianumcloud/talk/deleteMessage/deleteMessage.dart

@@ -11,7 +11,7 @@ class DeleteMessage extends TalkApi {
 
   @override
   assemble(String raw) {
-
+    return null;
   }
 
   @override

lib/api/marianumcloud/talk/deleteReactMessage/deleteReactMessage.dart

@@ -12,7 +12,7 @@ class DeleteReactMessage extends TalkApi {
 
   @override
   assemble(String raw) {
-
+    return null;
   }
 
   @override

lib/api/marianumcloud/talk/reactMessage/reactMessage.dart

@@ -12,7 +12,7 @@ class ReactMessage extends TalkApi {
 
   @override
   assemble(String raw) {
-
+    return null;
   }
 
   @override

lib/api/marianumcloud/talk/sendMessage/sendMessage.dart

@@ -11,7 +11,7 @@ class SendMessage extends TalkApi {
 
   @override
   assemble(String raw) {
-
+    return null;
   }
 
   @override