code: @Override
  	public String getImmutableValue() {
  		String value = null;
  		if (fixedValue != null) {
  			value = fixedValue;
  		} else if (currentValue != null) {
  			value = currentValue;
  		}
  		return value;
  	}
docs: In contrary to calling {@link #getValue()} this method does not use the underlying constraint
  for generating a value. Instead, only fixed value and current value are checked. The returned
  value is not processed using {@link Configuration#processPropertyValue(String)} and can also
  be null.
  
  @see com.mgmtp.jfunk.data.generator.util.ValueCallback#getImmutableValue()