docs: public FieldValue lookup(FieldName name){
  		Map<FieldName, FieldValue> values = getValues();
  
  		FieldValue value = values.getOrDefault(name, EvaluationContext.UNDECLARED_VALUE);
  		if(value != EvaluationContext.UNDECLARED_VALUE){
  			return value;
  		}
  
  		throw new MissingValueException(name);
  	}