amount null when getting address utxos

[Garbolino]

I am getting amount null when request to address utxos:

https://digiexplorer.info/api/addrs/dgb1qg6k8fvna9mmr8h0hwvv9hrscm2c6nsz6xrh4gp/utxo

result: [
{
address: "dgb1qg6k8fvna9mmr8h0hwvv9hrscm2c6nsz6xrh4gp",
txid: "7334312b2d43750026ebf195ff90866cc7090cd8b5b49321bb72b9af22bb91ad",
vout: 1,
ts: 1591893193,
scriptPubKey: "001446ac74b27d2ef633ddf773185b8e18dab1a9c05a",
amount: null,
confirmations: 6,
confirmationsFromCache: true
}
]

Any idea why?
Thanks!