fix: Illegal op_policy_uri parameter: - exclude entries with blank values from discovery response (oxauth counterpart)

[yuriyz]

Describe the issue

op_policy_uri being blank is causing a ParseException on large open source tools like spring oauth, and pac4j leveraging nimbusds. This value either needs to be removed all together or have a value in it.

oxauth counterpart GluuFederation/oxAuth#1823

Steps To Reproduce

Steps to reproduce the behavior:

1. Get an example project for spring oidc
2. attempt to login
3. receive error stating illegal op_policy_uri parameter

Screenshots

Desktop (please complete the following information):

• OS: Ubuntu 20
• Gluu version - 4.5.0.Final

Additional context

Here is the code that is being used within nimbusds that is throwing the error
if (jsonObject.get("op_policy_uri") != null) { try { as.setPolicyURI(JSONObjectUtils.getURI(jsonObject, "op_policy_uri")); } catch (IllegalArgumentException e) { throw new ParseException("Illegal op_policy_uri parameter: " + e.getMessage()); } }