Add test for validation of empty field definition
Add test for validation of empty field definition

dkellner/cerberus,funkyfuture/cerberus,dkellner/cerberus,brettatoms/cerberus,calve/cerberus,funkyfuture/cerberus,pyeve/cerberus,nicolaiarocci/cerberus,nicolaiarocci/cerberus,pyeve/cerberus,calve/cerberus,MacHu-GWU/cerberus-sanhe,MacHu-GWU/cerberus-sanhe