message with context is resolved properly when there is no cause defined

converter-CellDesigner/src/main/java/lcsb/mapviewer/converter/model/celldesigner/CellDesignerParserException.java

@@ -56,7 +56,13 @@ public abstract class CellDesignerParserException extends Exception {
   }
 
   public String getMessageWithContext() {
-    return getMessageContext() + " " + this.getCause().getMessage();
+    String message;
+    if (this.getCause() != null) {
+      message = this.getCause().getMessage();
+    } else {
+      message = this.getMessage();
+    }
+    return getMessageContext() + " " + message;
   }
 
   public abstract String getMessageContext();