Pull request overview

This pull request fixes an issue where delayed converter resolution for nullable arrays fails when null values precede non-null values. The problem occurred because null values in nullable arrays (e.g., DateTime?[]) were locking in the default type (timestamp), preventing subsequent non-null values that require a different type (timestamptz) from being properly resolved.

Changes:

• Fixed NullableConverter to return null instead of the default resolution for null values, allowing array converter to continue looking for non-null values
• Simplified ArrayConverter by removing special null handling (but introduces a regression)
• Added test case to verify null values can precede non-null values in nullable arrays

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/Npgsql/Internal/Converters/NullableConverter.cs	Changed GetEffectiveResolution to return null for null values instead of getting default resolution, enabling delayed resolution
src/Npgsql/Internal/Converters/ArrayConverter.cs	Removed special handling for null arrays and simplified switch statement structure (introduces bug for null arrays)
test/Npgsql.Tests/Types/DateTimeTests.cs	Added test case verifying that null can precede non-null DateTimeKind.Utc values in DateTime?[] arrays

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