title: java.lang.String android.os.Bundle.getString(java.lang.String)
body: <p>My MainActivity.class is invoking putExtra towards SecondActivity.class via setOnClickListener</p>
  
  <pre><code>Intent intent = new Intent(MainActivity.this, SecondActivity.class);
  intent.putExtra("sentString", stringName);
  startActivity(intent);
  </code></pre>
  
  <p>SecondActivity.class setOnClickListener</p>
  
  <pre><code>//    Recieve the extra sent from MainActivity.class
  Intent SecondActivityIntent = getIntent();
  String mString = SecondActivityIntent .getExtras().getString("sentString");
  
  //    Send extra to another activity ThirdActivity.class
  SecondActivityIntent.putExtra("sentString", mString);
  startActivity(SecondActivityIntent); 
  </code></pre>
  
  <p>ThirdActivity.class setOnClickListener</p>
  
  <pre><code>//    Recieve extra from SecondActivity.class
  Intent thirdActivityintent = getIntent();
  String mString = thirdActivityintent.getExtra().getString("sentString");
  //    This time I am calling SecondActivity.class but I will not send extra
  thirdActivityintent = new Intent(ThirdActivity.this, SecondActivity.class);
  startActivity(thirdActivityintent);
  </code></pre>
  
  <p>ThirdActivity.class is causing an </p>
  
  <blockquote>
    <p>'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference</p>
  </blockquote>
  
  <p>what does this error mean? Is it because SecondActivity.class is expecting to get an extra from any calling activity? I don't intend to putExtra on ThirdActivity or am I force to. How can this be solve?</p>