Android ExpandableListView NullPointerException в ObtainView

Я пытаюсь работать с простым ExpandableListView и не могу понять, почему я получаю этот NPE в ObtainView. У меня должен быть только один родитель и еще несколько дочерних элементов, которые должны открываться при нажатии на родителя из них, но он продолжает падать и показывать NullPointerException в ObtainView. Большое спасибо !

Prima.java:

package com.descoper.rom;

import java.util.ArrayList;

import android.app.ExpandableListActivity;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.widget.ExpandableListView;

public class Prima extends ExpandableListActivity
{
    // Create ArrayList to hold parent Items and Child Items
    private ArrayList<String> parentItems = new ArrayList<String>();
    private ArrayList<Object> childItems = new ArrayList<Object>();

    @Override
    public void onCreate(Bundle savedInstanceState) 
    {

        super.onCreate(savedInstanceState);


        // Create Expandable List and set it's properties
        ExpandableListView expandableList = getExpandableListView(); 
        expandableList.setDividerHeight(2);
        expandableList.setGroupIndicator(null);
        expandableList.setClickable(true);

        // Set the Items of Parent
        setGroupParents();
        // Set The Child Data
        setChildData();

        // Create the Adapter
        Adapter adapter = new Adapter(parentItems, childItems);

        adapter.setInflater((LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE), this);

        // Set the Adapter to expandableList
        expandableList.setAdapter(adapter);
        expandableList.setOnChildClickListener(this);
    }

    // method to add parent Items
    public void setGroupParents() 
    {
        parentItems.add("Categorii");
    }

    // method to set child data of each parent
    public void setChildData() 
    {

        // Add Child Items for Fruits
        ArrayList<String> child = new ArrayList<String>();
        child.add("Apple");
        child.add("Mango");
        child.add("Banana");
        child.add("Orange");

        childItems.add(child);

    }

}

Адаптер.java:

package com.descoper.rom;

import java.util.ArrayList;

import android.app.Activity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.CheckedTextView;
import android.widget.TextView;
import android.widget.Toast;

public class Adapter extends BaseExpandableListAdapter 
{

    private Activity activity;
    private ArrayList<Object> childtems;
    private LayoutInflater inflater;
    private ArrayList<String> parentItems, child;

    // constructor
    public Adapter(ArrayList<String> parents, ArrayList<Object> childern)
    {
        this.parentItems = parents;
        this.childtems = childern;
    }

    public void setInflater(LayoutInflater inflater, Activity activity) 
    {
        this.inflater = inflater;
        this.activity = activity;
    }

    // method getChildView is called automatically for each child view.
    public View getChildView1(int groupPosition, final int childPosition, boolean isLastChild, View convertView, ViewGroup parent) 
    {

        child = (ArrayList<String>) childtems.get(groupPosition);

        TextView textView = null;

        if (convertView == null) {
            convertView = inflater.inflate(R.layout.child, null);
        }

         // get the textView reference and set the value
        textView = (TextView) convertView.findViewById(R.id.textViewChild);
        textView.setText(child.get(childPosition));

        // set the ClickListener to handle the click event on child item
        convertView.setOnClickListener(new OnClickListener() {

            public void onClick(View view) {
                Toast.makeText(activity, child.get(childPosition),
                        Toast.LENGTH_SHORT).show();
            }
        });
        return convertView;
    }

    // method getGroupView is called automatically for each parent item
    public View getGroupView1(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) 
    {

        if (convertView == null) {
            convertView = inflater.inflate(R.layout.categorii, null);
        }

        ((CheckedTextView) convertView).setText(parentItems.get(groupPosition));
        ((CheckedTextView) convertView).setChecked(isExpanded);

        return convertView;
    }

    @Override
    public Object getChild(int groupPosition, int childPosition) 
    {
        return null;
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) 
    {
        return 0;
    }

    @Override
    public int getChildrenCount(int groupPosition) 
    {
        return ((ArrayList<String>) childtems.get(groupPosition)).size();
    }

    @Override
    public Object getGroup(int groupPosition) 
    {
        return null;
    }

    @Override
    public int getGroupCount() 
    {
        return parentItems.size();
    }

    @Override
    public void onGroupCollapsed(int groupPosition) 
    {
        super.onGroupCollapsed(groupPosition);
    }

    @Override
    public void onGroupExpanded(int groupPosition)
    {
        super.onGroupExpanded(groupPosition);
    }

    @Override
    public long getGroupId(int groupPosition) 
    {
        return 0;
    }

    @Override
    public boolean hasStableIds() 
    {
        return false;
    }

    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition)
    {
        return false;
    }

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded,
            View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public View getChildView(int groupPosition, int childPosition,
            boolean isLastChild, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        return null;
    }

}

родительский.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="@drawable/backg1"
    android:gravity="center|top"
     >

    <CheckedTextView 
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/textViewGroupName"
        android:layout_width="wrap_content"
        android:layout_height="60dp"
        android:layout_marginLeft="5dp"
        android:gravity="center_vertical"
        android:text="Categorii"
        android:textSize="18dp"
        android:textColor="#FFFFFF"
        android:padding="10dp"
        android:textStyle="bold" /> 

</LinearLayout>

ребенок.xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="40dp"

    android:clickable="true"
    android:orientation="vertical"
    android:paddingLeft="40dp"
     >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="39dp"
        android:gravity="center_vertical" >

        <ImageView
            android:id="@+id/childImage"
            android:layout_width="30dp"
            android:layout_height="30dp"
            android:layout_margin="5dp"
            android:background="@drawable/ic_launcher"
            android:contentDescription="@null" />

        <TextView
            android:id="@+id/textViewChild"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="5dp"
            android:text="Categorii"
            android:textSize="16sp"
            android:textColor="#1919A3"
            android:textStyle="bold" />
    </LinearLayout>

    <View
        android:layout_width="match_parent"
        android:layout_height="1dp"
        android:background="@android:color/white" />

</LinearLayout>

logcat:

05-19 10:18:25.180: E/AndroidRuntime(1361): FATAL EXCEPTION: main
05-19 10:18:25.180: E/AndroidRuntime(1361): Process: com.descoper.rom, PID: 1361
05-19 10:18:25.180: E/AndroidRuntime(1361): java.lang.NullPointerException
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.AbsListView.obtainView(AbsListView.java:2265)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.ListView.makeAndAddView(ListView.java:1790)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.ListView.fillDown(ListView.java:691)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.ListView.fillFromTop(ListView.java:752)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.ListView.layoutChildren(ListView.java:1630)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.AbsListView.onLayout(AbsListView.java:2091)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.View.layout(View.java:14817)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.ViewGroup.layout(ViewGroup.java:4631)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.View.layout(View.java:14817)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.ViewGroup.layout(ViewGroup.java:4631)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.View.layout(View.java:14817)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.ViewGroup.layout(ViewGroup.java:4631)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.View.layout(View.java:14817)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.ViewGroup.layout(ViewGroup.java:4631)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1987)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1744)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.Choreographer.doCallbacks(Choreographer.java:574)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.Choreographer.doFrame(Choreographer.java:544)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.os.Handler.handleCallback(Handler.java:733)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.os.Handler.dispatchMessage(Handler.java:95)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.os.Looper.loop(Looper.java:136)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at android.app.ActivityThread.main(ActivityThread.java:5017)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at java.lang.reflect.Method.invokeNative(Native Method)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at java.lang.reflect.Method.invoke(Method.java:515)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-19 10:18:25.180: E/AndroidRuntime(1361):     at dalvik.system.NativeStart.main(Native Method)