Allow [ShowIf] and [HideIf] to check for null

[boxrocket6803]

Summary

HideIfAttribute (and by extension ShowIfAttribute) previously wouldn't function when using null as the value, now they do.

Motivation & Context

slight annoyance, easy fix

Implementation Details

The entire SerializedObject was being passed into SerializedProperty.GetValue(object defaultValue) as the default (such that if the properties value was null it would check against the serialized object rather than the property and always return false). I'm assuming this to be unintentional.

Checklist

• Code follows existing style and conventions
• No unnecessary formatting or unrelated changes
• Public APIs are documented (if applicable)
• Unit tests added where applicable and all passing
• I’m okay with this PR being rejected or requested to change 🙂

[Copilot]

Pull request overview

Updates conditional inspector visibility attributes to correctly support null comparisons when evaluating against SerializedObject, aligning [HideIf] / [ShowIf] behavior with expected “value is null” checks in the Editor inspector.

Changes:

• Stop passing the SerializedObject instance as the defaultValue to SerializedProperty.GetValue<T>(), allowing null property values to remain null.
• Ensure [HideIf] / [ShowIf] can match Value == null as intended.

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[sboxbot]

This PR has been merged upstream.