It went something like:
niftynei: Hey, cppcheck complains this might be NULL, so I put in a check.
rusty: cppcheck is dumb. Make it an assert("Rusty always right!").
niftynei: You seem certain of this so I shall do that.
https://github.com/ElementsProject/lightning/pull/1994
...
renepickhardt: I asked fiatjaf to run
`lightning-cli sendpay "[{'id':'02db8f487fcc0a'}]" 4efe0ba89b`
and his node crashed!
rusty: grep Assertion logs/*
lightningd/jsonrpc.c:326: connection_complete_error: Assertion `Rusty is always right!' failed.
It turns out that in the 'can't parse' error case, we hand NULL cmd to
connection_compete_error.
Next time, less asserting, more grepping!
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>