code: public StrSubstitutor setValueDelimiter(final String valueDelimiter) {
          if (StringUtils.isEmpty(valueDelimiter)) {
              setValueDelimiterMatcher(null);
              return this;
          }
          return setValueDelimiterMatcher(StrMatcher.stringMatcher(valueDelimiter));
      }
docs: Sets the variable default value delimiter to use.
  <p>
  The variable default value delimiter is the character or characters that delimit the
  variable name and the variable default value. This method allows a string
  variable default value delimiter to be easily set.
  <p>
  If the <code>valueDelimiter</code> is null or empty string, then the variable default
  value resolution becomes disabled.
  
  @param valueDelimiter  the variable default value delimiter string to use, may be null or empty
  @return this, to enable chaining
  @since 3.2