07-25 15:31:26.758: E/AndroidRuntime(911): FATAL EXCEPTION: main
07-25 15:31:26.758: E/AndroidRuntime(911): java.lang.NullPointerException
07-25 15:31:26.758: E/AndroidRuntime(911):  at com.corsalini.david.calcolopesi.ActCalcolo.onCreateOptionsMenu(ActCalcolo.java:162)
07-25 15:31:26.758: E/AndroidRuntime(911):  at com.actionbarsherlock.app.SherlockActivity.onCreatePanelMenu(SherlockActivity.java:173)
07-25 15:31:26.758: E/AndroidRuntime(911):  at com.actionbarsherlock.ActionBarSherlock.callbackCreateOptionsMenu(ActionBarSherlock.java:556)
07-25 15:31:26.758: E/AndroidRuntime(911):  at com.actionbarsherlock.internal.ActionBarSherlockCompat.preparePanel(ActionBarSherlockCompat.java:483)
07-25 15:31:26.758: E/AndroidRuntime(911):  at com.actionbarsherlock.internal.ActionBarSherlockCompat.dispatchInvalidateOptionsMenu(ActionBarSherlockCompat.java:273)
07-25 15:31:26.758: E/AndroidRuntime(911):  at com.actionbarsherlock.internal.ActionBarSherlockCompat$1.run(ActionBarSherlockCompat.java:988)
07-25 15:31:26.758: E/AndroidRuntime(911):  at android.os.Handler.handleCallback(Handler.java:587)
07-25 15:31:26.758: E/AndroidRuntime(911):  at android.os.Handler.dispatchMessage(Handler.java:92)
07-25 15:31:26.758: E/AndroidRuntime(911):  at android.os.Looper.loop(Looper.java:123)
07-25 15:31:26.758: E/AndroidRuntime(911):  at android.app.ActivityThread.main(ActivityThread.java:3683)
07-25 15:31:26.758: E/AndroidRuntime(911):  at java.lang.reflect.Method.invokeNative(Native Method)
07-25 15:31:26.758: E/AndroidRuntime(911):  at java.lang.reflect.Method.invoke(Method.java:507)
07-25 15:31:26.758: E/AndroidRuntime(911):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
07-25 15:31:26.758: E/AndroidRuntime(911):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
07-25 15:31:26.758: E/AndroidRuntime(911):  at dalvik.system.NativeStart.main(Native Method)

public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getSupportMenuInflater();
    inflater.inflate(R.menu.menu_main, menu);
    MenuItem menuItem = menu.findItem(R.id.miShare);
    ShareActionProvider mShareActionProvider = (ShareActionProvider) menuItem.getActionProvider();
    // Set the default share intent
    Intent shareIntent = new Intent(Intent.ACTION_SEND);
    shareIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET);
    shareIntent.setType("text/plain");
    shareIntent.putExtra(Intent.EXTRA_TEXT, getString(R.string.share_text));
    shareIntent.putExtra(Intent.EXTRA_SUBJECT, getString(R.string.share_subject));
    mShareActionProvider.setShareIntent(shareIntent);  //Line 162
    return true;
}

<menu xmlns:android="http://schemas.android.com/apk/res/android" >
    <item
        android:id="@+id/miPref"
        android:icon="@drawable/ic_action_settings"
        android:showAsAction="ifRoom"
        android:title="@string/settings"
        android:visible="true" />
    <item
        android:id="@+id/miReset"
        android:icon="@drawable/ic_action_reset"
        android:showAsAction="ifRoom"
        android:title="@string/reset"
        android:visible="true" />
    <item
        android:id="@+id/miShare"
        android:actionProviderClass="android.widget.ShareActionProvider"
        android:showAsAction="ifRoom"
        android:title="@string/share" />
</menu>

android:actionProviderClass="com.actionbarsherlock.widget.ShareActionProvider"

menuItem.setActionProvider(mShareActionProvider);

android:actionProviderClass="com.actionbarsherlock.widget.ShareActionProvider"

<menu xmlns:android="http://schemas.android.com/apk/res/android" >
    <item
        android:id="@+id/miShare"
        android:actionProviderClass="com.actionbarsherlock.widget.ShareActionProvider"
        android:showAsAction="always"
        android:title="Share" />
</menu>

inflater.inflate(R.menu.temp_menu, menu);

mShareActionProvider.setShareHistoryFileName(ShareActionProvider.DEFAULT_SHARE_HISTORY_FILE_NAME);

ShareActionProvider mShareActionProvider = (ShareActionProvider) menuItem.getActionProvider();
Log.w("NullPointerException", "Is mShareActionProvider null: " + (mShareActionProvider == null));