private static Boolean isNullableConstantField(FieldScope field) {
        List<?> constantValues = ConstantValueModule.extractConstantFieldValue(field);
        if (constantValues == null) {
            return null;
        }
        return constantValues.get(0) == null;
    }
Determine whether the given field is a constant (i.e. static and final) and if so, indicant whether the constant value is null.

@param field targeted field
@return true/false depending on constant value being null; otherwise returning null if field is not a constant
jsonschema-generator/src/main/java/com/github/victools/jsonschema/generator/impl/module/ConstantValueModule.java