Merge pull request bitcoin#988 from dr-orlovsky/patch-1

BIP 174: require creator to initialize empty output fields

Author: luke-jr

bip-0174.mediawiki

@@ -431,7 +431,7 @@ Using the transaction format involves many different roles. Multiple roles can b
 ===Creator===
 
 The Creator creates a new PSBT. It must create an unsigned transaction and place it in the PSBT.
-The Creator must create empty input fields.
+The Creator must create empty input and output fields.
 
 ===Updater===