( Toolbar ) findViewById( R.id.tool_bar ) return NULL

My Android Studio, for some reason, started to default to a CustomView that would not allow me to edit the layout. It starts up with with a theme that includes a toolbar and mail icon in the bottom right. mainAcitivty.java is then looking for that toolbar and fab, which is no longer there.

in mainAcitivty.java REPLACE:

 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
}

WITH this

 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}