Resources update function results in Python HTTP request InvalidSchema error

I am calling nexussdk.resources.update on a resource created on Nexus sandbox (nexus-sandbox.io), and the function results in HTTP request results in InvalidSchema error: "No connection adapters were found for 'base:?rev=1'"

Here is the instance object that is used to send the request:

OrderedDict([('@context', ['https://nexus-sandbox.io/v1/resources/kcnitest/redcap/_/medredcontexttest10']), ('@id', 'initial_appointmen_arm_1'), ('_self', 'base:initial_appointmen_arm_1'), ('_constrainedBy', 'https://bluebrain.github.io/nexus/schemas/unconstrained.json'), ('_project', 'https://nexus-sandbox.io/v1/projects/kcnitest/redcap'), ('_rev', 1), ('_deprecated', False), ('_createdAt', '2019-02-12T15:53:26.937Z'), ('_createdBy', 'https://nexus-sandbox.io/v1/realms/github/users/ehsanmaag'), ('_updatedAt', '2019-02-12T15:53:26.937Z'), ('_updatedBy', 'https://nexus-sandbox.io/v1/realms/github/users/ehsanmaag'), ('title', 'Initial Appointment'), ('medred:includesInstrument', ['ex:patient_health_questionnaire_9'])])

It seems the reason is that instance["_self"] does not contain the full request URL.
How can we resolve that?

Start at nexussdk.resources.update and reproduce the request with the instance object shown in the issue. Trace how the _self value, especially the base:initial_appointmen_arm_1 form, becomes the request URL; done means the update no longer raises InvalidSchema for resources created on the Nexus sandbox.

Written by the indexing model from the issue text.