[AIRFLOW-5260] Allow empty uri arguments in connection strings

[sb2nov]

Allow empty string arguments in the connection string. This is needed if you're connecting to RDS using IAM role instead of a password then we would want to pass the aws_conn_id argument as empty.

Jira

• My PR addresses the following Airflow Jira issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-XXX
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Description

• Allow empty string arguments in the connection string. This is needed if you're connecting to RDS using IAM role instead of a password then we would want to pass the aws_conn_id argument as empty.

Tests

• Added unittest

Commits

• My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• [] In case of new functionality, my PR adds documentation that describes how to use it.
  • All the public functions and the classes in the PR contain docstrings that explain what it does
  • If you implement backwards incompatible changes, please leave a note in the Updating.md so we can assign it to a appropriate release

Code Quality

• Passes flake8

[mik-laj]

HI.
Your change is wonderful, but every code change needs a ticket. Can you create it?

Best

[sb2nov]

Thanks for the review, created the JIRA issue. Should be ready to merge now.

[kaxil]

Thanks @sb2nov