Android : Necessity to clear emulator data on increasing number of Tables in SQLiteDatabase Android

I have one minor doubt for which I was not able to get a satisfying answer. Here's the scenario:

I get a NPE during onCreate method of the OpenHelper class when I increase the number of tables in an already existing database , but when I run the same app after clearing the emulator data everything seems to run miraculously fine....

I have no idea why this happens, any explanation would be helpful....

public static final String DATABASE_NAME = "MONEY_DATABASE";
public static final String TABLE_NAME = "MONEY_TABLE";
public static final String TABLE_FIELDS = "FIELD_TABLE";

public static final int DATABASE_VERSION = 4;

public static final String KEY_ID = "_id";
public static final String KEY_AMOUNT = "amount";
public static final String KEY_DATE = "date_int";

public static final String KEY_TYPE_ID = "type_id";
public static final String KEY_TYPE = "type";
public static final String KEY_TITLE = "field_title";

Context localContext;

public HelperMethods (Context c)
{
    Log.d("dev","HelperMethods object created");
    this.localContext = c;
    localopenhelper = new OpenHelper(localContext);

    if(localContext == null)
    {
        Log.d("dev","localContext is null");
    }

}


public SQLiteDatabase database ;

class OpenHelper extends SQLiteOpenHelper
{
    // CREATE TABLE MONEY_TABLE ( _id INTEGER PRIMARY KEY AUTOINCREMENT, amount DOUBLE);

    private String query = "CREATE TABLE " + TABLE_NAME + " ( " + KEY_ID +  " INTEGER PRIMARY KEY AUTOINCREMENT, "
            + KEY_AMOUNT + " DOUBLE, " + KEY_DATE + " DOUBLE);";

    private String query1 = "CREATE TABLE " + TABLE_FIELDS + " ( " + KEY_TYPE_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
           + KEY_TYPE + " TEXT NOT NULL, " + KEY_TITLE + " TEXT NOT NULL);";

    Context helperContext;

    public OpenHelper(Context context)
    {
        super(context, DATABASE_NAME, null , DATABASE_VERSION);

        this.helperContext = context;

    }

    @Override
    public void onCreate(SQLiteDatabase db)
    {
        db.execSQL(query);

        db.execSQL(query1);
    }