Valid value: A value which is neither missing nor invalid.
Invalid value: The input value is not missing but it does not belong to a certain value range. The range of valid
values can be defined for each field.
Missing value: Input value is missing, for example, if a database column contains a null value. It is possible to
explicitly define values which are interpreted as missing values.
Linear Supertypes
Enumeration, Serializable, Serializable, AnyRef, Any