Fix: Allow calling methods with only output parameters

[Copilot]

Proposed changes

Fixes validation error when calling OPC UA methods that have only output parameters (no input parameters). The BinaryDecoder.ReadVariantArray() returns null for empty arrays (array length = -1 on wire), causing validation to incorrectly reject these valid method calls.

Changes:

• Modified MasterNodeManager.ValidateCallRequestItem() to initialize InputArguments to empty collection when null
• Added test coverage for methods with no input arguments

// Before: Would fail validation
var request = new CallMethodRequest 
{
    ObjectId = objectId,
    MethodId = methodId,
    // InputArguments decoded as null for methods with no inputs
};

// After: Validation initializes to empty collection
callMethodRequest.InputArguments ??= new VariantCollection();

Related Issues

• Fixes Call Method fail when method has only output parameter #2125

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which adds functionality)
• Test enhancement (non-breaking change to increase test coverage)
• Breaking change (fix or feature that would cause existing functionality to not work as expected, requires version increase of Nuget packages)
• Documentation Update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc.
• I have signed the CLA.
• I ran tests locally with my changes, all passed.
• I fixed all failing tests in the CI pipelines.
• I fixed all introduced issues with CodeQL and LGTM.
• I have added tests that prove my fix is effective or that my feature works and increased code coverage.
• I have added necessary documentation (if appropriate).
• Any dependent changes have been merged and published in downstream modules.

Further comments

The fix is minimal and surgical - only modifying validation to handle the null case that occurs during deserialization. All existing tests pass (156/156 Server tests), plus 3 new tests specifically validate the fix.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Call Method fail when method has only output parameter</issue_title>
<issue_description>### Type of issue

• Bug
• Enhancement
• Compliance
• Question
• Help wanted

Current Behavior

I need to call a method without input arguments. When I call it, the response is 'BadNothingToDo'. I tried with two different servers and different methods and it doesn't work

Expected Behavior

Return output arguments as UaExpert do.

Steps To Reproduce

No response

Environment

- OS: Windows 10
- Environment:
- Runtime:
- Nuget Version:
- Component:
- Server:
- Client:

Anything else?

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Call Method fail when method has only output parameter #2125

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[romanett]

@marcschier I am not against the fix & the test, but isnt this already fixed by a past decoder update?