DialogFragment is not displayed

I am trying to display a DialogFragment with a button so that when I press it, the dialogue simply disappears. It should be shown when a PlainText has no text in it but I can not get it to be displayed. What am I doing wrong?

At the moment I have this code:

public void registerUser(View view){
   TextView userText = findViewById(R.id.userText);
   if(userText.getText().toString().isEmpty()){
         InfoDialog infoDialog = new InfoDialog(getString(R.string.empty_userName));
         infoDialog.showDialog(infoDialog);
    }
}

The following is the code of my InfoDialog class

public class InfoDialog extends DialogFragment {

private String message;

public InfoDialog(){ }

public InfoDialog(String message) {
    super();
    this.message = message;
}

@Override
public Dialog onCreateDialog(Bundle savedInstanceState){
    //Use builder class for convenient dialog construction
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    builder.setMessage(message);
    builder.setPositiveButton(R.string.accept_message, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            dismiss();
        }
    });

    return builder.create();
}

public void showDialog(DialogFragment dialogFragment){
    dialogFragment.show(getFragmentManager(), "emptyUserDialog");
}

}

As far as I understand, the onCreateDialog method is called automatically or am I wrong?

Thank you in advance. Greetings