Fix exception in delegated admin code

Steps to recreate:

1. Install IDM
2. Create a managed user with userName demo and password Password1.
3. Run the test curl statement (result: 403)
4. curl --location --request GET 'http://localhost:8080/openidm/managed/user?_queryFilter=true' \ --header 'X-OpenIDM-Username: demo' \ --header 'X-OpenIDM-Password: Password1'
5. Go into the console, to manage internal roles.
6. Select openidm-authorized and add a privilege for the user above.
7. Select User and enter a demo, hit save.
8. Repeat the test curl (result: 200 with user info)
9. Change the mail attribute on the managed user to allow null values.
10. Repeat the test curl (result: 500)

Error seen in logs:

SEVERE: RuntimeException caughtSEVERE: RuntimeException caughtorg.forgerock.json.JsonValueException: /objects/0/schema/properties/mail/type: Expecting a java.lang.String at org.forgerock.json.JsonValue.expect(JsonValue.java:762)

Area of interest:
at org.forgerock.openidm.authz.DelegatedAdminFilter.attributeIsRelationship(DelegatedAdminFilter.java:371)
if (attrSchema.isDefined("type") && attrSchema.get("type").asString().equals("array")
&& attrSchema.isDefined("items") && attrSchema.get("items").isDefined("type")
&& attrSchema.get("items").get("type").asString().equals("relationship"))