I Have a lightning component from which I pass data to an apex class. I return the object. Why don't I get an update on my object neither a response in my lightning component.

Lightning 

```
updatePicklist : function(component,event,helper){ 
    var selectedValues = $('[id$=picklist]').select2("val");
    var field = component.get("v.fieldName");
    var object = component.get("v.objectName");
    var getCurrentRecord = component.get("v.recordId"); 
    var action = component.get("c.updateRecord");
    action.setParams({
        "objId": getCurrentRecord,
        "objNew": object,
        "selection" : selectedValues,
        "fieldName" : field
    });
    action.setCallback(this, function(response) {
        if (response.getState() == "SUCCESS") {
            alert('record Updated Successfully-->' + JSON.stringify(response.getReturnValue()));   
            //Fire the refresh view event to update detail view
            $A.get('e.force:refreshView').fire();
        }
    });
    $A.enqueueAction(action);
}

```

Apex

```
@AuraEnabled
public static sObject updateRecord(string objNew, id objId , string selection, string fieldName){
    sObject sObj = Schema.getGlobalDescribe().get(objNew).newSObject(objId) ;
    sObj.put(fieldName , selection) ;
    update sObj ;
    return sObj;
}

Logging
16:22:13.0 (161658)|CODE_UNIT_STARTED|[EXTERNAL]|Aura
16:22:13.0 (1468788)|CODE_UNIT_STARTED|[EXTERNAL]|01p1l0000008UC9|select2TestCtrl.updateRecord(String, Id, String, String)
16:22:13.0 (1708031)|SYSTEM_MODE_ENTER|false
16:22:13.0 (1828648)|USER_DEBUG|[19]|DEBUG|null null null null
16:22:13.0 (14355318)|FATAL_ERROR|System.NullPointerException: Attempt to de-reference a null object

Class.select2TestCtrl.updateRecord: line 20, column 1
16:22:13.0 (14381632)|FATAL_ERROR|System.NullPointerException: Attempt to de-reference a null object

Class.select2TestCtrl.updateRecord: line 20, column 1
16:22:13.0 (14398622)|CODE_UNIT_FINISHED|select2TestCtrl.updateRecord(String, Id, String, String)
16:22:13.0 (18207207)|CODE_UNIT_FINISHED|Aura
16:22:13.0 (19271021)|EXECUTION_FINISHED

```