Update omit zero when no fields produces invalid syntax

[mgazza]

pg/orm/update_test.go

Line 59 in 691def1

Expect(s).To(Equal(`UPDATE "update_tests" AS "update_test" SET WHERE "update_test"."id" = NULL`))

When updating and the model contains all empty fields invalid update syntax is produced.

Suggest returning specific error to capture the case of a non-update

[mgazza]

#1940