@JsonSetter (nulls = Nulls.AS_EMPTY)

[double-Nian]

@JsonSetter (nulls = Nulls.AS_EMPTY)
becomes ""
How to assign an enumeration
now protocol is null
I want to make "" become an enumeration

@JsonSetter(nulls = Nulls.AS_EMPTY)
private Constants.PROTO_TYPE protocol;

[cowtowncoder]

What exactly are you doing? What is the input, what kind of type is Constants? What becomes ""?

You are missing a lot of relevant information here to try to help.

[double-Nian]

@JsonSetter(nulls = Nulls.AS_EMPTY)
private Constants.PROTO_TYPE protocol;

when input {"protocol":null}
the enum Constants.PROTO_TYPE not accept
ask @JsonSetter any other way handle this question

[cowtowncoder]

Unfortunately that is no more useful information. Sorry, I can not really help here.