check whether variable is null does not pass - android java

I have a small problem that I don't understand:

When an activity of mine initializes is creates a variable like this:

Thread thread = null;

Then, somewhere later in an click event of my activity it checks:

if (thread == null) { }

this check however, does not pass.

This is my full code:

    package com.example.cheese.digiticsdomainchecker;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.StatusLine;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;


public class login extends Activity {
    ArrayList<String> domains = new ArrayList<String>();
    ArrayList<String> availables = new ArrayList<String>();
    ArrayList<String> selected = new ArrayList<String>();
    ArrayList<String> prices = new ArrayList<String>();
    String success;
    Thread thread = null;
    EditText etEmail;
    EditText etPassword;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        Intent intent = getIntent();
        domains = intent.getStringArrayListExtra("domainList");
        prices = intent.getStringArrayListExtra("priceList");
        availables = intent.getStringArrayListExtra("availableList");
        selected = intent.getStringArrayListExtra("selectedList");
        etEmail = (EditText) findViewById(R.id.etEmail);
        etPassword = (EditText) findViewById(R.id.etPassword);
    }

    public void btRegister_Click(View v) {
        Intent registerView = new Intent(this, register.class);
        startActivity(registerView);
    }

    public void btLogin_click(View v) {
        if (etEmail.getText().toString() != "" && etPassword.getText().toString() != "") {
            if (thread == null) {
                    thread = new Thread(new Runnable() {
                        @Override
                        public void run() {
                            try {
                                LoginJSON();
                            } catch (Exception e) {
                                login.this.runOnUiThread(new Runnable() {
                                    public void run() {
                                        Toast.makeText(login.this, "ik ben niet zomaar een haas, ik ben een vis.", Toast.LENGTH_SHORT).show();
                                    }
                                });
                                e.printStackTrace();
                            }
                        }
                    });
            } else {
                Toast.makeText(login.this, thread.toString(), Toast.LENGTH_SHORT).show();
            }
        }
    }

    public String md5(String s) {
        try {
            // Create MD5 Hash
            MessageDigest digest = java.security.MessageDigest.getInstance("MD5");
            digest.update(s.getBytes());
            byte messageDigest[] = digest.digest();

            // Create Hex String
            StringBuffer hexString = new StringBuffer();
            for (int i=0; i<messageDigest.length; i++)
                hexString.append(Integer.toHexString(0xFF & messageDigest[i]));
            return hexString.toString();

        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        return "";
    }

    public void LoginJSON() {
        Boolean bok = false;
        String email = etEmail.getText().toString();
        String password = etPassword.getText().toString();
        try {
            StringBuilder builder = new StringBuilder();
            HttpClient client = new DefaultHttpClient();
            HttpGet httpGet = new HttpGet("http://ift.tt/1EMkKix"+email+"&password="+md5(password));
            HttpResponse response = client.execute(httpGet);
            StatusLine statusLine = response.getStatusLine();
            int statusCode = statusLine.getStatusCode();
            if (statusCode == 200) {
                HttpEntity entity = response.getEntity();
                InputStream content = entity.getContent();
                BufferedReader reader = new BufferedReader(new InputStreamReader(content));
                String line;
                while ((line = reader.readLine()) != null) {
                    builder.append(line);
                }
            } else {
                login.this.runOnUiThread(new Runnable() {
                    public void run() {
                        Toast.makeText(login.this, "Verbinden met server mislukt.", Toast.LENGTH_SHORT).show();
                    }
                });
            }

            String rawJsonData = builder.toString();
            JSONObject jsonObject = new JSONObject(rawJsonData); // CONVERT TO JSON OBJECT
            JSONArray resultArray = jsonObject.getJSONArray("LOGIN"); //GET MAIN JSON ITEM
            for (int i = 0; i < resultArray.length(); i++){ //LOOP THROUGH MAIN JSON ITEM
                JSONObject jsonSubResult = resultArray.getJSONObject(i); //GET ITEM AT SPECIFIC INDEX
                success = jsonSubResult.getString("COMPLETED");
            }
        } catch(Exception e) {
            bok = true;
        }

        if(bok == false) {
            thread = null;
            switch(success){
                case "YES":
                    //LOCAL STORAGE
                    SharedPreferences prefs = this.getSharedPreferences("com.example.rubenurresti.digiticsdomainchecker", Context.MODE_PRIVATE);
                    prefs.edit().putString("email", email).apply();
                    prefs.edit().putString("password", md5(password)).apply();

                    //Intent registerView = new Intent(this, order.class);
                    //registerView.putExtra("domainList", domains);
                    //registerView.putExtra("priceList", prices);
                    //registerView.putExtra("availableList", availables);
                    //registerView.putExtra("selectedList", selected);
                    //startActivity(registerView);
                    login.this.runOnUiThread(new Runnable() {
                        public void run() {
                            Toast.makeText(login.this, "ik ben een haas.", Toast.LENGTH_SHORT).show();
                        }
                    });
                    break;
                default:
                    login.this.runOnUiThread(new Runnable() {
                        public void run() {
                            Toast.makeText(login.this, "Foute gegevens.", Toast.LENGTH_SHORT).show();
                        }
                    });
                    break;
            }
        } else {
            thread = null;
            login.this.runOnUiThread(new Runnable() {
                public void run() {
                    Toast.makeText(login.this, "Onverwachte fout.", Toast.LENGTH_SHORT).show();
                }
            });
        }
    }
}