[management] Error when trying to access Design menu with new design studio and without admin rights

[micedre]

As an api_publisher, when adding a new API with Design Studio and trying to access the design menu, we got a red alert and the page doesn't display.

Expected Behavior

The design page is usable.

Current Behavior

I got the following error in UI : Internal Server Error.
In the management logs I have this stacktrace :

09:10:58.884 [gravitee-listener-226] ERROR i.g.r.a.m.r.provider.ThrowableMapper - Internal error
java.lang.NullPointerException: null
    at io.gravitee.rest.api.service.impl.MembershipServiceImpl.getUserMemberPermissions(MembershipServiceImpl.java:870)
    at jdk.internal.reflect.GeneratedMethodAccessor758.invoke(Unknown Source)

Steps to Reproduce (for bugs)

https://nightly.gravitee.io/ , with api1 user, create an api with design studio and try to open the design page.
Or just use this one : https://nightly.gravitee.io/#!/apis/88616aac-db5d-46a0-a16a-acdb5d46a0ff/portal

Your Environment

• Version used: 3.5.1 (docker)
• Browser Name and version: Firefox 78.6.1esr
• Operating System and version: Windows 10