message: Return None if insufficient finality signatures.
diff: @@ -1608,7 +1608,7 @@ impl Storage {
  Some(block_header) => block_header,
  };
  let block_signatures = match self.get_sufficient_finality_signatures(tx, &block_header)? {
  - None => BlockSignatures::new(*block_hash, block_header.era_id()),
  + None => return Ok(None),
  Some(signatures) => signatures,
  };
  Ok(Some(BlockHeaderWithMetadata {
  