Android : Android - Pass Data Between Two Activities get NullPointerException

I have 3 activities we will call them A, B and C. A and B both have intents that send the view to C. And design on which one C came from different things happen on C's activity. I pass the data like this from A to C:

Intent intent = new Intent(this, C.class);
    intent.putExtra("Action", "A");
    startActivity(intent);

Then in C's onCreate method I have something like this:

Bundle extras = getIntent().getExtras();
if (extras.getString("Action").equals("A")) {
//DO SOMETHING
}

Then I from B to C I have

 Intent intent = new Intent(this, C.class);
 startActivity(intent);

And then I get the NullPointerException, I am guessing this is because i have not specifed a String "Action" when going from B to C.

Now I could just add one line for B in this case but, if there were for more activities or a large project this would not be good, because for each activity going to one I would need this.

How can I have it so I don't get this exception without adding an "Action" sting to activity B?

Thanks for the help in advance.