Schema metadata does not show "null" if the metadata value is null

## Describe the bug
Metadata can have a valid value of `null` but when schema view shows the metadata it only prints the key

## To Reproduce
Steps to reproduce the behaviour OR commands run:
1. Have null as the value for default key in the metadata
2. Check Fields view -> metadata for the field

## Expected behaviour
I would expect null to be shown

## Screenshots
**For**
```json
"metadata" : {
"default" : null
}
```
**shows**