Fix null pointer exception

src/main/java/com/btk5h/skriptdb/skript/EffExecuteStatement.java

@@ -305,6 +305,7 @@ public class EffExecuteStatement extends Effect {
     private void setVariable(Event e, String name, Object obj) {
 
         //fix mediumblob and similar column types, so they return a String correctly
+        if (obj != null) {
             if (obj.getClass().getName().equals("[B")) {
                 obj = new String((byte[]) obj);
 
@@ -316,6 +317,7 @@ public class EffExecuteStatement extends Effect {
                     ex.printStackTrace();
                 }
             }
+        }
         Variables.setVariable(name.toLowerCase(Locale.ENGLISH), obj, e, isLocal);
     }