support default namespace for list api

[nianliuu]

Problem

in pinecone, the default namespace is "", the check in list will throw exception if namespace is ""

Solution

remove the empty namespace check, only check namespace is null

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

./gradlew build, passed all tests

[nianliuu]

@russcam can anyone help have a look of this PR? thank you!

[rohanshah18]

@nianliuu thank you for creating the PR, I have ran the integration test. Once successful, I'll approve the PR.

[nianliuu]

The API key is required and must not be empty or null, looks like API-Key not set for IT @rohanshah18

[rohanshah18]

I was able to successfully run the integration tests with these changes, LGTM! Once again, thank you for creating the PR.