Make relation Filtering None-tolerant for maximal flexibility

[peterallenwebb]

resolves #8974

Problem

Spark needs flexibility to have None/null value for the database identifier.

Solution

We now explicitly allow that.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (bb21403) 86.46% compared to head (baf83a2) 86.51%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8975      +/-   ##
==========================================
+ Coverage   86.46%   86.51%   +0.05%     
==========================================
  Files         179      179              
  Lines       26505    26508       +3     
==========================================
+ Hits        22917    22933      +16     
+ Misses       3588     3575      -13     

Flag	Coverage Δ
integration	83.40% <100.00%> (+0.12%)	⬆️
unit	64.81% <100.00%> (+<0.01%)	⬆️

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Files	Coverage Δ
core/dbt/adapters/base/impl.py	82.93% <100.00%> (+0.07%)	⬆️

... and 3 files with indirect coverage changes

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