It's not possible to get a value from ezdate fieldtype when using GraphQL.
Steps to reproduce:
1. Login as admin
2. Create a new Content Type named "MyDate"
3. Add ezdate fieldtype
4. Create a Content Item using that Content Type
5. Regenerate GraphQL schema and clear cache
6. Enter following query:
timestamp field causes an error:
format return null - the same query for ezdateandtime fieldtype returns correct values, so something must be wrong with the format option as well (it should return the specified day.