request object before returning an error so that id value can
be used in the response.
Prior to this commit, RPC commands sent during Bitcoin's
warmup/startup phase were responded to with a JSON-RPC error
with an id of null, which violated the JSON-RPC 2.0 spec:
id: This member is REQUIRED. It MUST be the same as the value
of the id member in the Request Object. If there was an error
in detecting the id in the Request object (e.g. Parse
error/Invalid Request), it MUST be Null.
getmemorypool [data]
If [data] is not specified, returns data needed to construct a block to work on:
"version" : block version
"previousblockhash" : hash of current highest block
"transactions" : contents of non-coinbase transactions that should be included in the next block
"coinbasevalue" : maximum allowable input to coinbase transaction, including the generation award and transaction fees
"time" : timestamp appropriate for next block
"bits" : compressed target of next block
If [data] is specified, tries to solve the block and returns true if it was successful.