The issue root cause was from a noob lack of understanding: It was assumed that the datasources proxied through JRS. So no datasource defined on the server would work for a typical deployment configuration where the server is in AWS and the datasources are in AWS. Though the MSSQLServer datasource was inspectable in Studio (either community or pro), the AWS datasource was not, and the NPE was distracting. The AWS datasource should be inspectable even if it cannot be used locally due to firewalls and AWS IAM security. The ultimate solution is to not expect to use datasources locally in an AWS deployment configuration. The report designer should instead rely on a domain that was previously created. Domains are working fine for both MSSQLServer and AWS RDS datasources.
