Replace empty value in dictionary Kusto

I have this data:

let data = datatable(Timestamp:datetime, Name:string, Value:int)
            [
             datetime(2022-02-18 10:00:00 AM), "Floor 1", 100,
            ];
    let mydict = dynamic(
        {
             "Id":"1",
             "Product": ""
        }
    );
data
| extend messageMetaData = mydict
| project Timestamp, Name, Value, messageMetaData = replace_string(tostring(messageMetaData), "", "Wheat")

What I am trying to achieve here is to replace the empty value in messageMetaData by a string. When running this code it is giving me the exact same result/

Expected result:

>Solution :

print mydict = dynamic({"Id":"1", "Product": ""})
| extend messageMetaData = replace_string(tostring(mydict), '""', '"Wheat"')

Fiddle