问读取浏览器历史记录时发生致命异常

EN

private static final Uri BOOKMARKS_URI = null;
private static final String[] HISTORY_PROJECTION = null;
private static final int HISTORY_PROJECTION_TITLE_INDEX = 0;
private static final int HISTORY_PROJECTION_URL_INDEX = 0;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.browser);

    mWebView = (WebView) findViewById(R.id.webview);
    mWebView.getSettings().setJavaScriptEnabled(true);
    mWebView.getSettings().setBuiltInZoomControls(true);
    mWebView.loadUrl(turl);

    mWebView.setWebViewClient(new BrowserClient() {

        public void onPageFinished(WebView view, String url) {
            getBrowserHist();
        } 
    });
    }
    public void getBrowserHist()  {
       Cursor mCur = managedQuery(Browser.BOOKMARKS_URI, Browser.HISTORY_PROJECTION, null, null, null);
       mCur.moveToFirst();
       if (mCur.moveToFirst() && mCur.getCount() > 0) {
            while (mCur.isAfterLast() == false) {
                 Log.v("titleIdx", mCur.getString(Browser.HISTORY_PROJECTION_TITLE_INDEX));
                 Log.v("urlIdx", mCur.getString(Browser.HISTORY_PROJECTION_URL_INDEX));
                 mCur.moveToNext();
            }
        }
     }

   12-27 11:50:55.122: ERROR/AndroidRuntime(295): FATAL EXCEPTION: main
   12-27 11:50:55.122: ERROR/AndroidRuntime(295): java.lang.NullPointerException
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at android.content.ContentResolver.acquireProvider(ContentResolver.java:727)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at                                    android.content.ContentResolver.query(ContentResolver.java:239)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at android.app.Activity.managedQuery(Activity.java:1520)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at com.mobila.browser.Browser.getBrowserHist(Browser.java:108)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at com.mobila.browser.Browser$1.onPageFinished(Browser.java:70)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at android.webkit.CallbackProxy.handleMessage(CallbackProxy.java:274)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at android.os.Handler.dispatchMessage(Handler.java:99)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at android.os.Looper.loop(Looper.java:123)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at android.app.ActivityThread.main(ActivityThread.java:4627)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at java.lang.reflect.Method.invokeNative(Native Method)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at java.lang.reflect.Method.invoke(Method.java:521)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
   12-27 11:50:55.122: ERROR/AndroidRuntime(295):     at dalvik.system.NativeStart.main(Native Method)