Fix a crashing bug

Signed-off-by: Mario Danic <mario@lovelyhq.com>

app/build.gradle

@@ -15,8 +15,8 @@ android {
         targetSdkVersion 27
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
 
-        versionCode 53
-        versionName "3.0.0beta2"
+        versionCode 54
+        versionName "3.0.0beta3"
 
         flavorDimensions "default"
         renderscriptTargetApi 19

app/src/main/java/com/nextcloud/talk/models/json/converters/EnumSystemMessageTypeConverter.java

@@ -80,6 +80,10 @@ public class EnumSystemMessageTypeConverter extends StringBasedTypeConverter<Cha
     @Override
     public String convertToString(ChatMessage.SystemMessageType object) {
 
+        if (object == null) {
+            return "";
+        }
+
         switch (object) {
             case CONVERSATION_CREATED:
                 return "conversation_created";