Distinguish null from empty string for UUID deserialization

For UUID deserialization, empty string is mapped to null by FromStringDeserializer. So something like {"parent_uuid": null} can’t be distinguished from {"parent_uuid": ""}. From the view of a strict API, the latter is an error. It would be good to add some feature like “STRICT_STRING_VALUE”, that FromStringDeserializer does not trim or shortcut empty strings so that UUID deserializer could report the error. This may be an opposite feature of #768 ACCEPT_EMPTY_STRING_AS_NULL_OBJECT.

[cowtowncoder]

So, implemented using new “CoercionConfigs” system; test CoerceMiscScalarsTest has full verification for UUID as well as other types. Default behavior in 2.12 NOT changed.

To make coercion from empty String fail only for UUID, you can use:

ObjectMapper mapper = ...;
mapper.coercionConfigFor(UUID.class)
    .setCoercion(CoercionInputShape.EmptyString, CoercionAction.Fail);

or to change handling of most similar scalar types:

ObjectMapper mapper = ...;
mapper.coercionConfigFor(LogicalType.OtherScalar)
    .setCoercion(CoercionInputShape.EmptyString, CoercionAction.Fail);

or, even, if you really want, prevent it by most types (unless overridden by more-specific setting:

ObjectMapper mapper = ...;
mapper.coercionConfigDefaults()
    .setCoercion(CoercionInputShape.EmptyString, CoercionAction.Fail);

Alternatively you can use CoercionAction.AsNull to allow coercion to null, or, CoercionAction.AsEmpty to get “all-zeroes” UUID constructed.

[shahaf-sameach]

hi, new contributor 😃 can I try this one?