code: public static char getTrigger(final String delimitedExpression) {
          final String expr = StringUtils.trimToEmpty(delimitedExpression);
          Validate.isTrue(isDelimited(expr));
          return expr.charAt(0);
      }
docs: Get the trigger character for the specified delimited expression.
  
  @param delimitedExpression
  @return first non-whitespace character of {@code delimitedExpression}
  @throws IllegalArgumentException if argument expression is not delimited