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

lib/view/pages/timetable/arbitraryAppointment.dart

@@ -6,7 +6,7 @@ class ArbitraryAppointment {
   GetTimetableResponseObject? webuntis;
   CustomTimetableEvent? custom;
 
-  ArbitraryAppointment({this.webuntis, this.custom}) {}
+  ArbitraryAppointment({this.webuntis, this.custom});
 
   bool hasWebuntis() {
     return webuntis != null;