code: @Override
      public StringValue getParameterValue(final String _name)
      {
          final List<StringValue> values = this.parameters.get(_name);
          return (values != null && !values.isEmpty()) ? values.get(0)
                          : StringValue.valueOf((String) null);
      }
docs: Returns single value for parameter with specified name. This method always returns non-null
  result even if the parameter does not exist.
  
  @param _name parameter name
  @return {@link StringValue} wrapping the actual value