Add null check for host in Amazon Redshift connection

[sunank200]

This is a bug in the current implementation as per the PR.

When user passes the following as part of redshift connection, it would break:

{
  "iam": true,
  "cluster_identifier": "redshift-cluster-1",
  "port": 5439,
  "region": "us-east-1",
  "db_user": "awsuser",
  "database": "dev",
  "profile": "default"
}

The following image shows that the host is not set in the connection but cluster_identifier is set.

Even though the cluster_identifier is set here this would break with the following error on the line as host is not set because conn.host is evaluated first and when we split it to NoneType object it would throw attribute error.

conn.extra_dejson.get("cluster_identifier", conn.host.split(".")[0])

Following is the test we did.

>>> conn.extra_dejson.get("cluster_identifier")
PyDev console: starting.
'<REDSHIFT_CLUSTER_IDENTIFIER>'
>>> conn.extra_dejson.get("cluster_identifier", None)
'<REDSHIFT_CLUSTER_IDENTIFIER>'
>>> conn.host

>>> conn.extra_dejson.get("cluster_identifier", conn.host.split(".")[0])
Traceback (most recent call last):
  File "/Applications/PyCharm.app/Contents/plugins/python/helpers/pydev/_pydevd_bundle/pydevd_exec2.py", line 3, in Exec
    exec(exp, global_vars, local_vars)
  File "<input>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'split'

This is a bug in the current implementation for all users when host is not set in the connection (not only for default connections). This would require a null check for conn.host.

closes: #31551
Added a null check for conn.host. conn.host.split(".")[0] is compiled regardless of the extra values.

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[phanikumv]

can you add tests for this change please

[hussein-awala]

Could you add a test for this fix to test the different cases (loading from cluster_identifier, loading from host and raising an exception if both are not preset)?

[ashb]

Tests please!

[sunank200]

Tests please!

@phanikumv @ashb @hussein-awala added the test cases here: 4e643c3

[hussein-awala]

I just pushed a commit to simplify the tests, you can change it if you think that there is something missing