[net11] Templates: Fix duplicate Empty/empty parameter crash in maui-blazor templates by Copilot · Pull Request #34609 · dotnet/maui

Copilot · 2026-03-23T21:58:33Z

Note

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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. Thank you!

Root Cause

The maui-blazor and maui-blazor-web template.json files defined two symbols with effectively the same name: Empty (PascalCase) and empty (lowercase). This was intentional when added in #32227 — Empty was kept as a hidden backward-compat alias for users who had used the old CLI flag.

However, .NET 11's templating engine now performs case-insensitive key comparison when loading template symbols, causing it to throw:

System.ArgumentException: An item with the same key has already been added. Key: empty

This makes dotnet new maui-blazor and dotnet new maui-blazor-web completely broken.

Description of Change

maui-blazor/.template.config/template.json: Remove the duplicate "Empty" (PascalCase) parameter block.
maui-blazor-solution/.template.config/template.json: Remove the duplicate "Empty" (PascalCase) parameter block.
SampleContent computed expression (both files): Simplified from (!Empty && ...) && (!empty && ...) to just !empty && ... since the Empty alias is gone.

No other templates were found to have duplicate case-insensitive parameter keys.

Issues Fixed

Related: dotnet/templating#10025

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Copilot

Pull request overview

Removes a case-insensitive duplicate template parameter (Empty vs empty) from the MAUI Blazor templates to prevent System.ArgumentException failures in newer .NET SDK templating when parsing template.json.

Changes:

Removed the deprecated Empty boolean parameter from both Blazor template template.json files.
Updated the SampleContent computed symbol expressions to rely only on empty for dotnet CLI hosts.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Templates/src/templates/maui-blazor/.template.config/template.json	Removes `Empty` symbol and updates `SampleContent` computed expression to use only `empty`.
src/Templates/src/templates/maui-blazor-solution/.template.config/template.json	Removes `Empty` symbol and updates `SampleContent` computed expression to use only `empty`.

Comments suppressed due to low confidence (2)

src/Templates/src/templates/maui-blazor/.template.config/template.json:173

Empty was removed from this template’s symbols, but src/Templates/src/templates/maui-blazor/.template.config/dotnetcli.host.json still contains symbolInfo for Empty. That entry is now stale and can be removed to keep the CLI host configuration aligned with the template’s symbols (and avoid future confusion about whether --Empty is supported).

    "empty": {
      "type": "parameter",
      "datatype": "bool",
      "defaultValue": "false",
      "description": "Configures whether to omit sample pages and styling that demonstrate basic usage patterns."

src/Templates/src/templates/maui-blazor-solution/.template.config/template.json:411

Empty was removed from this template’s symbols, but src/Templates/src/templates/maui-blazor-solution/.template.config/dotnetcli.host.json still contains symbolInfo for Empty. That entry is now stale and can be removed to keep the CLI host configuration aligned with the template’s symbols (and avoid future confusion about whether --Empty is supported).

    "empty": {
      "type": "parameter",
      "datatype": "bool",
      "defaultValue": "false",
      "description": "Configures whether to omit sample pages and styling that demonstrate basic usage patterns."

github-actions · 2026-03-23T22:29:21Z

🚀 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 -- 34609

Or

Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 34609"

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

src/Templates/src/templates/maui-blazor-solution/.template.config/template.json:412

After removing the Empty symbol, the template’s localization files still contain symbols/Empty/description entries but no symbols/empty/description. This can leave the --empty parameter without localized help text (or cause stale localization keys to linger). Regenerate/update .template.config/localize/templatestrings*.json so the description is keyed to empty.

    "IncludeSampleContent": {
      "type": "parameter",
      "datatype": "bool",
      "defaultValue": "true",
      "displayName": "_Include sample pages",
      "description": "Configures whether to add sample pages and styling to demonstrate basic usage patterns."
    },
    "empty": {
      "type": "parameter",
      "datatype": "bool",
      "defaultValue": "false",
      "description": "Configures whether to omit sample pages and styling that demonstrate basic usage patterns."
    },

Copilot · 2026-03-24T18:15:21Z

src/Templates/src/templates/maui-blazor/.template.config/template.json

    "IncludeSampleContent": {
      "type": "parameter",
      "datatype": "bool",
      "defaultValue": "true",
      "displayName": "_Include sample pages",
      "description": "Configures whether to add sample pages and styling to demonstrate basic usage patterns."
    },
-    "Empty": {
-      "type": "parameter",
-      "datatype": "bool",
-      "defaultValue": "false",
-      "description": "Configures whether to omit sample pages and styling that demonstrate basic usage patterns."
-    },
    "empty": {
      "type": "parameter",
      "datatype": "bool",
      "defaultValue": "false",
      "description": "Configures whether to omit sample pages and styling that demonstrate basic usage patterns."
    },


After removing the Empty symbol, the template’s localization files still only define symbols/Empty/description (and there is no symbols/empty/description). This likely means the --empty option’s description won’t be localized (or will be looked up under a stale key). Regenerate/update the .template.config/localize/templatestrings*.json entries to use the empty symbol key instead of Empty.

mattleibow · 2026-03-24T18:51:30Z

⚠️ Merge Conflict Detected — This PR has merge conflicts with its target branch. Please rebase onto the target branch and resolve the conflicts.

Co-authored-by: mattleibow <1096616+mattleibow@users.noreply.github.com> Agent-Logs-Url: https://github.com/dotnet/maui/sessions/5d92997c-8acf-44d6-8eb7-bc127a174184

The Empty parameter was removed from template.json but references remained in the dotnetcli.host.json files for both maui-blazor and maui-blazor-solution templates. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Rename the localization key to match the remaining lowercase 'empty' parameter after the PascalCase 'Empty' duplicate was removed. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

mattleibow · 2026-03-24T19:50:20Z

⚠️ Merge Conflict Detected — This PR has merge conflicts with its target branch. Please rebase onto the target branch and resolve the conflicts.

mattleibow · 2026-03-25T15:10:44Z

/backport to release/11.0.1xx-preview3

github-actions · 2026-03-25T15:10:54Z

Started backporting to release/11.0.1xx-preview3 (link to workflow run)

@mattleibow

…pty parameter crash in maui-blazor templates (#34646) Backport of #34609 to release/11.0.1xx-preview3 /cc @mattleibow @Copilot --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: mattleibow <1096616+mattleibow@users.noreply.github.com> Co-authored-by: Matthew Leibowitz <mattleibow@live.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot AI assigned Copilot and mattleibow Mar 23, 2026

Copilot created this pull request from a session on behalf of mattleibow March 23, 2026 21:59 View session

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Copilot finished work on behalf of mattleibow March 23, 2026 22:23

mattleibow changed the base branch from main to net11.0 March 23, 2026 22:27

mattleibow force-pushed the copilot/fix-templates-and-build branch from 7566d3e to bce0075 Compare March 23, 2026 22:29

Copilot started work on behalf of mattleibow March 23, 2026 22:29 View session

Copilot finished work on behalf of mattleibow March 23, 2026 22:44

mattleibow changed the title ~~Fix duplicate Empty/empty parameters in MAUI Blazor template.json files~~ [net11] Templates: Fix duplicate Empty/empty parameter crash in maui-blazor templates Mar 23, 2026

github-actions bot mentioned this pull request Mar 24, 2026

[repo-status] Daily Repo Status - March 24, 2026 #34612

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mattleibow marked this pull request as ready for review March 24, 2026 18:03

mattleibow requested a review from Copilot March 24, 2026 18:11

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Copilot AI and others added 3 commits March 24, 2026 21:49

Fix duplicate Empty/empty parameters in maui-blazor template.json files

996046f

Co-authored-by: mattleibow <1096616+mattleibow@users.noreply.github.com> Agent-Logs-Url: https://github.com/dotnet/maui/sessions/5d92997c-8acf-44d6-8eb7-bc127a174184

Fix localization keys: symbols/Empty → symbols/empty in templatestrings

9ce8709

Rename the localization key to match the remaining lowercase 'empty' parameter after the PascalCase 'Empty' duplicate was removed. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

mattleibow force-pushed the copilot/fix-templates-and-build branch from e22344e to 9ce8709 Compare March 24, 2026 19:49

mattleibow merged commit 3deb096 into net11.0 Mar 25, 2026
26 of 31 checks passed

mattleibow deleted the copilot/fix-templates-and-build branch March 25, 2026 15:10

github-actions bot mentioned this pull request Mar 25, 2026

[release/11.0.1xx-preview3] [net11] Templates: Fix duplicate Empty/empty parameter crash in maui-blazor templates #34646

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[net11] Templates: Fix duplicate Empty/empty parameter crash in maui-blazor templates#34609

[net11] Templates: Fix duplicate Empty/empty parameter crash in maui-blazor templates#34609
mattleibow merged 3 commits intonet11.0from
copilot/fix-templates-and-build

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