title: RecyclerView is null
body: <p>The main activity : </p>
  
  <pre><code>public class MainActivity extends AppCompatActivity {
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
          setSupportActionBar(toolbar);
  
          recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
  
          pAdapter = new ProductAdapter(productList);
          RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
          recyclerView.setLayoutManager(mLayoutManager);
      }
  </code></pre>
  
  <p>I am getting this error : </p>
  
  <pre><code>java.lang.RuntimeException: Unable to start activity ComponentInfo{in.co.thehawker.thehawker/in.co.thehawker.thehawker.MainActivity}: java.lang.NullPointerException
                                                                                 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2114)
                                                                                 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2139)
                                                                                 at android.app.ActivityThread.access$700(ActivityThread.java:143)
                                                                                 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1241)
                                                                                 at android.os.Handler.dispatchMessage(Handler.java:99)
                                                                                 at android.os.Looper.loop(Looper.java:137)
                                                                                 at android.app.ActivityThread.main(ActivityThread.java:4960)
                                                                                 at java.lang.reflect.Method.invokeNative(Native Method)
                                                                                 at java.lang.reflect.Method.invoke(Method.java:511)
                                                                                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
                                                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
                                                                                 at dalvik.system.NativeStart.main(Native Method)
                                                                              Caused by: java.lang.NullPointerException
                                                                                 at in.co.thehawker.thehawker.MainActivity.onCreate(MainActivity.java:36)
  </code></pre>
  
  <p>content_main.xml</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;RelativeLayout
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      app:layout_behavior="@string/appbar_scrolling_view_behavior"
      tools:showIn="@layout/activity_main"
      tools:context=".MainActivity"&gt;
  
      &lt;android.support.v7.widget.RecyclerView
          android:id="@+id/recycler_view"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:scrollbars="vertical" /&gt;
  
  &lt;/RelativeLayout&gt; 
  </code></pre>
  
  <p>I cleaned and built the project, but problem remains the same. Is there some issue with activity_main layout as I have defined the recycler_view in content_main.xml? Please help!!!</p>
  
  <p>Edited:
  activity_main.xml</p>
  
  <pre><code>&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      tools:context=".MainActivity"&gt;
  
      &lt;LinearLayout
          android:layout_width="fill_parent"
          android:layout_height="wrap_content"
          android:layout_alignParentTop="true"
          android:orientation="vertical"&gt;
  
          &lt;include
              android:id="@+id/toolbar"
              layout="@layout/toolbar" /&gt;
      &lt;/LinearLayout&gt;
  
  
  &lt;/RelativeLayout&gt;
  </code></pre>