Fix for imageIds in Conferences

The API returns "" if there is no image. Before this commit, using the main constructor and passing empty strings for imageType and imageId lead to the value of ":" for image, which could cause comparison problems

Author: rubengees

library/src/main/java/com/proxerme/library/connection/messenger/entity/Conference.java

@@ -4,6 +4,7 @@
 import android.os.Parcelable;
 import android.support.annotation.IntRange;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.afollestad.bridge.annotations.Body;
 import com.proxerme.library.interfaces.IdItem;
@@ -55,20 +56,25 @@ public Conference[] newArray(int size) {
     }
 
     public Conference(@NonNull String id, @NonNull String topic, @NonNull String customTopic,
-                      @IntRange(from = 2) int participantAmount, @NonNull String imageType,
-                      @NonNull String imageId, boolean isGroup, boolean isRead, long time,
+                      @IntRange(from = 2) int participantAmount, @Nullable String imageType,
+                      @Nullable String imageId, boolean isGroup, boolean isRead, long time,
                       @IntRange(from = 0) int unreadMessageAmount,
                       @NonNull String lastReadMessageId) {
         this.id = id;
         this.topic = topic;
         this.customTopic = customTopic;
         this.participantAmount = participantAmount;
-        this.image = imageType + ":" + imageId;
         this.isGroup = isGroup;
         this.isRead = isRead;
         this.time = time;
         this.unreadMessageAmount = unreadMessageAmount;
         this.lastReadMessageId = lastReadMessageId;
+
+        if (imageType == null || imageType.isEmpty() || imageId == null || imageType.isEmpty()) {
+            this.image = "";
+        } else {
+            this.image = imageType + ":" + imageId;
+        }
     }
 
     protected Conference(Parcel in) {