Fix JSON unmarshalling of nulls [#3212]
- Closes #3212 (closed).
- Fixes custom (generated) JSON unmarshallers so they don't panic if an array value is null.
- Updates API v3 major block range query to return an empty range instead of not found.
- Fixes API v2's query-tx wait loop.
Changelog: fix
Edited by Ethan Reesor