The fields on Schema, show as int32 and undefined. Is it because of null values in some of the documents, does the fields show as Undefined.?
If a collection contains documents in which not all fields contain a value, the missing values display as undefined . Refer to https://docs.mongodb.com/compass/master/schema/
Correct. When a document in a collection has null value for a field, in schema view, that field value is categorised/displayed as undefined type.