fuzz: refactor: Replace NullUniValue with UniValue{}
fuzz: refactor: Replace NullUniValue with UniValue{}

This is needed for the scripted-diff to compile in the next commit

Xekyo/bitcoin,fanquake/bitcoin,bitcoin/bitcoin,AkioNak/bitcoin,mruddy/bitcoin,sipsorcery/bitcoin,namecoin/namecoin-core,kallewoof/bitcoin,tecnovert/particl-core,lateminer/bitcoin,ajtowns/bitcoin,AkioNak/bitcoin,lateminer/bitcoin,namecoin/namecoin-core,kallewoof/bitcoin,ajtowns/bitcoin,jambolo/bitcoin,sstone/bitcoin,bitcoinsSG/bitcoin,bitcoinsSG/bitcoin,fanquake/bitcoin,mruddy/bitcoin,jamesob/bitcoin,bitcoin/bitcoin,Xekyo/bitcoin,jamesob/bitcoin,sstone/bitcoin,jambolo/bitcoin,sipsorcery/bitcoin,lateminer/bitcoin,mruddy/bitcoin,bitcoin/bitcoin,tecnovert/particl-core,bitcoin/bitcoin,mruddy/bitcoin,bitcoinsSG/bitcoin,fanquake/bitcoin,namecoin/namecore,ajtowns/bitcoin,fujicoin/fujicoin,particl/particl-core,lateminer/bitcoin,fanquake/bitcoin,tecnovert/particl-core,mruddy/bitcoin,namecoin/namecoin-core,AkioNak/bitcoin,tecnovert/particl-core,bitcoin/bitcoin,jamesob/bitcoin,namecoin/namecoin-core,particl/particl-core,ajtowns/bitcoin,namecoin/namecore,particl/particl-core,lateminer/bitcoin,AkioNak/bitcoin,lateminer/bitcoin,tecnovert/particl-core,bitcoinsSG/bitcoin,bitcoin/bitcoin,ajtowns/bitcoin,bitcoinsSG/bitcoin,jambolo/bitcoin,sstone/bitcoin,kallewoof/bitcoin,namecoin/namecoin-core,jamesob/bitcoin,fujicoin/fujicoin,AkioNak/bitcoin,sipsorcery/bitcoin,sipsorcery/bitcoin,kallewoof/bitcoin,particl/particl-core,fujicoin/fujicoin,fanquake/bitcoin,sipsorcery/bitcoin,Xekyo/bitcoin,fanquake/bitcoin,sipsorcery/bitcoin,jambolo/bitcoin,Xekyo/bitcoin,namecoin/namecoin-core,namecoin/namecore,Xekyo/bitcoin,kallewoof/bitcoin,sstone/bitcoin,namecoin/namecore,fujicoin/fujicoin,sstone/bitcoin,jamesob/bitcoin,mruddy/bitcoin,particl/particl-core,jambolo/bitcoin,particl/particl-core,namecoin/namecore,jamesob/bitcoin,kallewoof/bitcoin,Xekyo/bitcoin,fujicoin/fujicoin,namecoin/namecore,fujicoin/fujicoin,tecnovert/particl-core,AkioNak/bitcoin,sstone/bitcoin,bitcoinsSG/bitcoin,jambolo/bitcoin,ajtowns/bitcoin