fix sending attachments(image) in open groups

libsession/src/main/java/org/session/libsession/messaging/opengroups/OpenGroupAPI.kt

@@ -113,7 +113,7 @@ object OpenGroupAPI: DotNetAPI() {
                                 val id = attachmentAsJSON["id"] as? Long ?: (attachmentAsJSON["id"] as? Int)?.toLong() ?: (attachmentAsJSON["id"] as String).toLong()
                                 val contentType = attachmentAsJSON["contentType"] as String
                                 val size = attachmentAsJSON["size"] as? Int ?: (attachmentAsJSON["size"] as? Long)?.toInt() ?: (attachmentAsJSON["size"] as String).toInt()
-                                val fileName = attachmentAsJSON["fileName"] as String
+                                val fileName = attachmentAsJSON["fileName"] as? String
                                 val flags = 0
                                 val url = attachmentAsJSON["url"] as String
                                 val caption = attachmentAsJSON["caption"] as? String

libsession/src/main/java/org/session/libsession/messaging/opengroups/OpenGroupMessage.kt

@@ -74,7 +74,7 @@ data class OpenGroupMessage(
                         attachment.id,
                         attachment.contentType!!,
                         attachment.size.orNull(),
-                        attachment.fileName.orNull(),
+                        attachment.fileName.orNull() ?: "",
                         0,
                         attachment.width,
                         attachment.height,