REST API responds with invalid JSON for Cache with values of type Instant

Issue

• Our Java application uses a cache with ProtoStream encoding and stores values of type Instant and keys of type String: RemoteCache<String, Instant>
  When we try to use the REST API (or the DataGrid web console), we get an invalid JSON response (cause of a missing value):

sh-4.4$ curl -k -u {user} "https://****:11222/rest/v2/caches/{cache_name}?action=entries&content-negotiation=true"
Enter host password for user {user}:
[{"key":{"_type":"string","_value":"5860b1e0b9ba589cfdb73ea0d9286bfb"},"value":}]

The issue also affects the Data grid web console:
The "Manage entries" tab shows an empty list, and the browser console shows JSON parsing errors.