[net11.0][iOS] Fix CS8604 build break in BlazorWebViewHandler header marshaling

[praveenkumarkarunanithi]

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue.

Root Cause

PR #35706 added an iOS helper, GetRequestHeaders, which reads request headers from an NSDictionary and passes them to the shared cache-policy code as KeyValuePair<string, string> entries. The implementation calls .ToString() on the dictionary key and value.

Although the key and value objects were already null-checked, NSObject.ToString() is itself nullable. The compiler therefore could not guarantee that the resulting strings were non-null when constructing KeyValuePair<string, string>, resulting in CS8604 on net11.0.

This was only a warning on net10.0, but the stricter nullable analysis in net11.0 promoted it to an error and caused the CI build failure.

Description of Change

Null-checked the  .ToString()  results via an inline  is string  pattern-match before yielding them. Semantically identical to the original loop with no behavior or performance impact — it only makes the nullable flow explicit to the compiler.

Issues Fixed

Fixes the net11.0 CI build failure caused by CS8604 in  BlazorWebViewHandler.iOS.cs

Regression Details

Regression from #35706

Platforms Tested

• iOS
• MacCatalyst
• Android
• Windows

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 37260

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 37260"

[azure-pipelines]

Azure Pipelines:
Successfully started running 1 pipeline(s).
There may be pipelines that require an authorized user to comment /azp run to run.

[azure-pipelines]

Azure Pipelines:
Successfully started running 1 pipeline(s).
There may be pipelines that require an authorized user to comment /azp run to run.

[Copilot]

Pull request overview

Fixes a net11.0-only nullable analysis build break (CS8604) in the iOS BlazorWebViewHandler request-header marshaling path by making the ToString() nullability explicit before constructing KeyValuePair<string,string> entries.

Changes:

• Updates GetRequestHeaders to pattern-match key?.ToString() and headers[key]?.ToString() into non-null string locals before yielding.
• Avoids passing potentially-null ToString() results into KeyValuePair<string,string> (resolving the compiler error under stricter net11.0 analysis).