allow nullable facts for ud.NewFromBackup in bindings

bindings/ud.go

@@ -144,8 +144,8 @@ func LoadOrNewUserDiscovery(e2eID int, follower UdNetworkStatus,
 // Parameters:
 //  - e2eID - e2e object ID in the tracker
 //  - follower - network follower func wrapped in UdNetworkStatus
-//  - emailFactJson - a JSON marshalled email fact.Fact
-//  - phoneFactJson - a JSON marshalled phone fact.Fact
+//  - emailFactJson - nullable JSON marshalled email fact.Fact
+//  - phoneFactJson - nullable JSON marshalled phone fact.Fact
 func NewUdManagerFromBackup(e2eID int, follower UdNetworkStatus, emailFactJson,
 	phoneFactJson []byte) (*UserDiscovery, error) {
 
@@ -156,15 +156,19 @@ func NewUdManagerFromBackup(e2eID int, follower UdNetworkStatus, emailFactJson,
 	}
 
 	var email, phone fact.Fact
+	if emailFactJson != nil {
 		err = json.Unmarshal(emailFactJson, &email)
 		if err != nil {
 			return nil, err
 		}
+	}
 
+	if phoneFactJson != nil {
 		err = json.Unmarshal(phoneFactJson, &phone)
 		if err != nil {
 			return nil, err
 		}
+	}
 
 	UdNetworkStatusFn := func() xxdk.Status {
 		return xxdk.Status(follower.UdNetworkStatus())