Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.s

Bonjour,
Voici une erreur que j'ai rencontré et dont je n'arrive pas à me débarrasser :

Code:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

Que dois-je faire ? Je vous poste mon code ci dessous, Merci ! ( problème ligne 18 )

Code:

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public class entery_names extends AppCompatActivity {
 
    RelativeLayout layout;
    RelativeLayout.LayoutParams params;
    Button mBtn_add_et;
    int id;
    int i;
    static int previousid;
 
    @SuppressLint("NewApi")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //Submit = (Button)loginDialog.findViewById(R.id.Submit);
        mBtn_add_et = findViewById(R.id.btn_add_et);
 
        mBtn_add_et.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (id <= 4) {
                    EditText et = new EditText(entery_names.this);
                    id = View.generateViewId();
                    et.setId(id);
                    layout = findViewById(R.id.relativeLayout);
                    params = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
                    params.addRule(RelativeLayout.BELOW, id);
                    if (previousid == 0)
                        params.addRule(RelativeLayout.BELOW, R.id.et3);
                    else
                        params.addRule(RelativeLayout.BELOW, previousid);
                    previousid = et.getId();
                    et.setHint("Enter Name");
                    et.setHintTextColor(getResources().getColor(R.color.colorTransparentWhite));
                    et.setTextColor(getResources().getColor(R.color.colorTransparentWhite));
                    et.setX(findViewById(R.id.et1).getX());
                    layout.addView(et, params);
                }
            }
        });
    }
}