Allow a pointer to be removed using GraphQL

[cjbland]

New Feature / Enhancement Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.

Current Limitation

I'm trying to clear out a column that currently has a pointer value. For example, I have a class named "Issue" and a field on that class is "user" which is defined as a pointer to the "_User" class. Once that field is set, I can never unset it using GraphQL

Feature / Enhancement Description

The current way to set a pointer on a field with GraphQL is: user: { link: 'myuserid' }. My suggestion (which I will submit a PR for) is to use something like: user: { unlink: true}. Looking through the code, this should be a pretty good and non-invasive use-case.

Example Use Case

Alternatives / Workarounds

My current work around is to issue a REST API call to clear out the field.

3rd Party References

[Moumouls]

Unlink pointer is supported by parse following GQL convention

mutation aMutation($anID: ID!) {
			updateSomething(
				input: {
					id: $anID
					fields: { somePointer: { link: null } }
				}
			) {
				someThing {
					id
				}
			}
		}