   (string, optional) delay processing request until the result would vary significantly from the "longpollid" of a prior template
       "data": "hex",          (string, optional) proposed block data to check, encoded in hexadecimal; valid only for mode="proposal"
     }

Result (If the proposal was accepted with mode=='proposal'):
null    (json null)

Result (If the proposal was not accepted with mode=='proposal'):
"str"    (string) According to BIP22

Result (Otherwise):
{                                