Given each field, determine whether it can be added to the serdes function
and, more importantly, determine how it should be added. If the field should not
be added, return null.
External models, such as REST or I/O, pull type inference data from class constructors.
This is to allow for class constructors to process potentially nullable data
into non-nullable data by assigning a default at initialization, or to allow a class
to process one type into another at construction (eg String myString -> Foo(myString)).
Sqlite data, however, is always serialized from dart -- as a result, we don't care about
mismatches between the constructor and member fields, and will always use the type defined
by the class member.
The field's value when used by the generator.
For example, data['my_field'] when used by a deserializing generator
or instance.myField when used by a serializing generator