The nullable package provides a number of types that represent values
that may be null. The standard Go library already includes types in the
database/sql package for this purpose including NullBool,
NullFloat64, NullInt64 and NullString.
The types in this package add to this list for convenience. The other
significant difference is that the types in this package all implement
the json.Marshaler and json.Unmarshaler interfaces, which are
used for serializing to and from JSON.