How Validate null data from SQLite in Splash Screen

I got a null value in my SQlite Database, but when I try to get this value... my app stopped

This is the code:

SplashScreenActivity.java

File dbtest =new File("data/data/http://ift.tt/1A6CZdr");
            if(dbtest.exists())
            {

                //This is the reason for my app crash: get the "null" value
                boolean tag= Check.beginActivity();

                if (tag==true){
                    Intent mainIntent = new Intent().setClass(SplashScreenActivity.this, ActivityVistaQR.class);
                    startActivity(mainIntent);
                }else{
                    Intent mainIntent = new Intent().setClass(SplashScreenActivity.this, ActivityVistaQR.class);
                    startActivity(mainIntent);
                }

            }
            else
            {
                Intent mainIntent = new Intent().setClass(SplashScreenActivity.this, HomeActivity.class);
                startActivity(mainIntent);

            }

beginActivity.java

public class RevisionInicio {

public static boolean beginActivity(){

    String tag= UsersDataBaseAdapter.getTag();

    if(Tag==null){
        return false;
    }else{
        return true;
    }

}

When the Database have a "null" value in "Tag" (in Users Table) my app Crash, when my Method get the value. What Should I do? Encode or Parse that value? (How?), Good Day :)