Describe the bug

If partition tag set empty string, the message returned should be

  reason: "Invalid partition tag:  Partition tag should not be empty."

Search failed:
status {
  error_code: ILLEGAL_ARGUMENT
  reason: "Invalid partition tag: . Partition tag should not be empty."
}

Steps/Code to reproduce behavior

Expected behavior

**Env

Describe the feature

I think enforcing typing in methods parameters can be helpful for robustness, readability and stability of the code.

By using mypy static type checker, we can see potential improvements for jina:

Usage:

pip install mypy
mypy --ignore-missing-imports jina

Do not get overwhelmed by the errors. Let's slowly keep improving until we can eve