code: public String getDigitPattern() {
          String pattern = Optional.fromNullable(getParameter(SignalParameters.DIGIT_PATTERN.symbol())).or("");
          if (!pattern.isEmpty()) {
              // Replace pattern to comply with MEGACO digitMap
              pattern = pattern.replace(".", "*").replace("x", "\\d");
          }
          return pattern;
      }
docs: A legal digit map as described in <a href="https://tools.ietf.org/html/rfc2885#section-7.1.14">section 7.1.14</a> of the
  MEGACO protocol using the DTMF mappings associated with the Megaco DTMF Detection Package described in the Megaco
  protocol document.
  <p>
  <b>This parameter should not be specified if one or both of the Minimum # Of Digits parameter and the Maximum Number Of
  Digits parameter is present.</b>
  </p>
  
  @return The digit pattern or an empty String if not specified.