Fix null reference and XML escaping in XmlDocumentationGenerator

[Copilot]

Description:

Addresses review feedback from PR #887 regarding null safety and XML encoding in XML documentation generation.

Null Reference Fix:

• Added null-conditional operator for document.Tags access to prevent NullReferenceException when OpenAPI document has no tags

XML Escaping Enhancement:

• Extended EscapeSymbols method to escape & character (in addition to existing < and >)
• Ensures proper encoding order: ampersand first, then angle brackets, to avoid double-escaping
• Prevents malformed XML when documentation contains special characters

Test Coverage:

• Can_Handle_Null_Document_Tags - validates safe handling of null tags collection
• Can_Escape_Xml_Special_Characters_In_Interface_Doc - verifies XML entity encoding in interface summaries
• Can_Escape_Xml_Special_Characters_In_Method_Summary - verifies XML entity encoding in method documentation

Example OpenAPI Specifications:

openapi: 3.0.0
info:
  title: Test API
paths:
  /users:
    get:
      summary: Get users <admin> & filter
      tags:
        - Users
      responses:
        '200':
          description: Success

Example generated Refit interface

Before:

/// <summary>Get users <admin> & filter</summary>  // Invalid XML
[Get("/users")]
Task GetUsers();

After:

/// <summary>Get users &lt;admin&gt; &amp; filter</summary>  // Valid XML
[Get("/users")]
Task GetUsers();

Warning

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• collector.exceptionless.io
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• heartbeat.exceptionless.io
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  • Triggering command: /home/REDACTED/work/refitter/refitter/src/Refitter.Tests/bin/Release/net8.0/Refitter.Tests /home/REDACTED/work/refitter/refitter/src/Refitter.Tests/bin/Release/net8.0/Refitter.Tests --server dotnettestcli --dotnet-test-pipe /tmp/cc8db2bd32014527829c9449c50731fa 607570477388aac361639dd7b0/Project.csproj (dns block)
• petstore.swagger.io
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  • Triggering command: /home/REDACTED/work/refitter/refitter/src/Refitter.Tests/bin/Release/net8.0/Refitter.Tests /home/REDACTED/work/refitter/refitter/src/Refitter.Tests/bin/Release/net8.0/Refitter.Tests --server dotnettestcli --dotnet-test-pipe /tmp/cc8db2bd32014527829c9449c50731fa 607570477388aac361639dd7b0/Project.csproj (dns block)
• petstore3.swagger.io
  • Triggering command: /home/REDACTED/work/refitter/refitter/src/Refitter.Tests/bin/Release/net8.0/Refitter.Tests /home/REDACTED/work/refitter/refitter/src/Refitter.Tests/bin/Release/net8.0/Refitter.Tests --server dotnettestcli --dotnet-test-pipe /tmp/d7f4e169f85e40a6a990ba2a40dd3467 (dns block)
  • Triggering command: /home/REDACTED/work/refitter/refitter/src/Refitter.Tests/bin/Release/net8.0/Refitter.Tests /home/REDACTED/work/refitter/refitter/src/Refitter.Tests/bin/Release/net8.0/Refitter.Tests --server dotnettestcli --dotnet-test-pipe /tmp/cc8db2bd32014527829c9449c50731fa 607570477388aac361639dd7b0/Project.csproj (dns block)

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Original prompt

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.33%. Comparing base (f049330) to head (9a8b9de).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #890   +/-   ##
=======================================
  Coverage   93.33%   93.33%           
=======================================
  Files          23       23           
  Lines        1395     1396    +1     
=======================================
+ Hits         1302     1303    +1     
  Misses         47       47           
  Partials       46       46           

Flag	Coverage Δ
unittests	93.33% <100.00%> (+<0.01%)	⬆️

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