Remove redundant field initialization in Java code.

chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappAuthenticator.java

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser.webapps;
 
 import android.annotation.SuppressLint;
 import android.content.Context;
 import android.os.AsyncTask;
 import android.os.StrictMode;
@@ skipping 29 matching lines @@
  * installed web apps and arbitrary other URLs.
  */
 public class WebappAuthenticator {
     private static final String TAG = "WebappAuthenticator";
     private static final String MAC_ALGORITHM_NAME = "HmacSHA256";
     private static final String MAC_KEY_BASENAME = "webapp-authenticator";
     private static final int MAC_KEY_BYTE_COUNT = 32;
     private static final Object sLock = new Object();
 
     private static FutureTask<SecretKey> sMacKeyGenerator;
-    private static SecretKey sKey = null;
+    private static SecretKey sKey;
 
     private static final TimesHistogramSample sWebappValidationTimes = new TimesHistogramSample(
             "Android.StrictMode.WebappAuthenticatorMac", TimeUnit.MILLISECONDS);
 
     /**
      * @see #getMacForUrl
      *
      * @param url The URL to validate.
      * @param mac The bytes of a previously-calculated MAC.
      *
@@ skipping 175 matching lines @@
             }
             Mac mac = Mac.getInstance(MAC_ALGORITHM_NAME);
             mac.init(key);
             return mac;
         } catch (GeneralSecurityException e) {
             Log.w(TAG, "Error in creating MAC instance", e);
             return null;
         }
     }
 }