fix: clustering_information panic if string domain is none

[zhyass]

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Summary

The cause of this panic is that the default domain maximum for String types is NULL. Therefore, wrapping the String type in a Nullable is necessary to handle this correctly.

• fixes: bug: panic viewing clustering_information with a <8 character cluster key #16763

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

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 could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

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This change is 

[dantengsky]

@zhyass

LGTM, besides: seems you are using a different version of py code formatter black ?