Handle null FieldName in FieldIdentifier.GetHashCode#66409
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MohamedOthman1 wants to merge 2 commits intodotnet:mainfrom
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Handle null FieldName in FieldIdentifier.GetHashCode#66409MohamedOthman1 wants to merge 2 commits intodotnet:mainfrom
MohamedOthman1 wants to merge 2 commits intodotnet:mainfrom
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The public constructor rejects null fieldName, but `default(FieldIdentifier)` bypasses it and leaves both Model and FieldName as null. Calling GetHashCode on that default value invoked StringComparer.Ordinal.GetHashCode(null), which throws ArgumentNullException with the message "Value cannot be null. (Parameter 'obj')" — surfaced by callers such as EditContext.NotifyFieldChanged. Guard against the null FieldName so dictionary lookups and Equals comparisons work for default-valued instances. Model is already safe because RuntimeHelpers.GetHashCode returns 0 for null. Fixes dotnet#45096
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Pull request overview
Fixes a crash when default(FieldIdentifier) is used as a dictionary key (or otherwise hashed) by making FieldIdentifier.GetHashCode() resilient to a null FieldName, which can occur when the struct is default-initialized (bypassing the constructor).
Changes:
- Guard
FieldIdentifier.GetHashCode()againstFieldName == nullto preventArgumentNullException. - Add regression tests ensuring default
FieldIdentifierhashing/equality works and it can be used as a dictionary key.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| src/Components/Forms/src/FieldIdentifier.cs | Prevents GetHashCode() from throwing when FieldName is null on a default struct value. |
| src/Components/Forms/test/FieldIdentifierTest.cs | Adds regression coverage for hashing/equality and dictionary usage of default(FieldIdentifier). |
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This was referenced Apr 22, 2026
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Summary
Fixes #45096.
FieldIdentifieris areadonly structwhose public constructor rejectsnullforfieldName. However,default(FieldIdentifier)bypasses the constructor and leavesModelandFieldNameasnull. CallingGetHashCode()on that default value invokesStringComparer.Ordinal.GetHashCode(null), which throws:This surfaces via any caller that hashes a default-valued
FieldIdentifier— most commonlyEditContext.NotifyFieldChanged, which uses aDictionary<FieldIdentifier, FieldState>keyed on the identifier. The repro in the issue hits this when a component callsEditContext.NotifyFieldChanged(FieldIdentifier)before itsValueExpressionhas been assigned.Fix
Guard
FieldIdentifier.GetHashCode()against a nullFieldName.Modelis already safe becauseRuntimeHelpers.GetHashCode(null)returns0and does not throw.Equalsalso already handles null viastring.Equals(..., StringComparison.Ordinal), so no change is needed there.This is a root-cause fix at the struct level, so every consumer (
NotifyFieldChanged,MarkAsUnmodified,GetValidationMessages(FieldIdentifier),IsValid(FieldIdentifier), etc.) benefits automatically — rather than adding a guard at each public entry point.Tests
Added three tests to
FieldIdentifierTestcoveringdefault(FieldIdentifier):DefaultFieldIdentifier_GetHashCode_DoesNotThrow— regression test against the original crash.DefaultFieldIdentifiers_AreEqual— verifies consistent equality / hash between two default values.DefaultFieldIdentifier_CanBeUsedAsDictionaryKey— mirrors the real-worldEditContextusage.Full
Microsoft.AspNetCore.Components.Forms.Testssuite: 81 passed, 0 failed locally.