Masih Error

package com.example.badruszamans.tugasakhir;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import org.json.JSONException;
import org.json.JSONObject;

import java.util.HashMap;
import java.util.Map;

public class MainActivity extends AppCompatActivity {

    EditText username, password;
    Button login;

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

        username =(EditText)findViewById(R.id.Username);
        password =(EditText)findViewById(R.id.Password);

        login = (Button)findViewById(R.id.LogIn);

        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
               String user = username.getText().toString();
               String pass = password.getText().toString();
                if (!user.isEmpty() && !pass.isEmpty()){
                    RequestLogin(user, pass);
                }else{
                    Toast.makeText(MainActivity.this, "Email dan Password harus diisi", Toast.LENGTH_SHORT).show();

                }
            }
        });
    }

        public void RequestLogin(String username, String password) {
        String url = "192.168.56.1/project/pendataan/login.php";

        StringRequest postRequest = new StringRequest(Request.Method.POST, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        try {
                            boolean jsonResponse = new JSONObject(response).getBoolean("error");
                            if (!jsonResponse){
                                Intent LogIn = new Intent(MainActivity.this, MainMenuActivity.class);
                                startActivity(LogIn);
                            }else {
                                Toast.makeText(MainActivity.this, "Maaf username atau password salah", Toast.LENGTH_SHORT).show();
                            }
                        } catch (JSONException e) {
                            Toast.makeText(MainActivity.this, "Maaf Json Error " + e.toString(), Toast.LENGTH_SHORT).show();
                            e.printStackTrace();
                        }
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        Toast.makeText(MainActivity.this, "Maaf Json Erro gan " + error.toString(), Toast.LENGTH_SHORT).show();
                        error.printStackTrace();
                    }
                }
        ) {
            @Override
            protected Map<String, String> getParams()
            {
                Map<String, String> params = new HashMap<>();
                // the POST parameters:
                params.put("user", "username");
                params.put("pass", "password");
                return params;
            }
        };
        Volley.newRequestQueue(this).add(postRequest);
    }
    }