In the wallet class make a test to know if it's an TX_NULL_DATA.
In the main class make a test to know if outputValue is zero (0) so no spent info possible.

Finally I decided to verify about a zero value. But maybe it is more clean the check in the CSpentIndexValue structure about the addressType instead of satoshis.

Just updated the changes log and the versioning to 2.0.8-1
This node is actually ruining on https://explorer.btcz.app

By verifying if the spent index exist in the block tree, I modified the return error to only if it's an valid address. I guess it's the best way to still get back the error (that should never happen) without trigger the OP_RETURN code.
Not necessary to check for more and it also avoid a false return !

    // In either case, we need to get more info ...
    if (!pblocktree->ReadSpentIndex(key, value)) {

      // Check if its an OP_RETURN code. GITHUB ISSUE #71
      // Only return error if it's a valid address
      CTxDestination dest = DestFromAddressHash(value.addressType, value.addressHash);
      if (IsValidDestination(dest)) {
        return error("Unable to get spent index information");
      }
    }

@cryptorex we could take this base for deprecation update. I tested it on FN wallet, BWS and explorer. But not on mining nodes... will check in mining-pool channel if someone is ready to test it.

Replaced by #99