private static String whereClauseForIssuer(String issuer) {
    if (issuer != null) {
      return ISSUER_COLUMN + " = " + DatabaseUtils.sqlEscapeString(issuer);
    }
    return ISSUER_COLUMN + " IS NULL";
  }
Creates a SQL {@code WHERE} clause for an issuer.

@param issuer may be {@code null}
@return an appropriate SQLite {@code WHERE} clause for this {@code issuer}
java/com/google/android/apps/authenticator/otp/AccountDb.java