[BUG]: CS0854 Compiler Error When Using Optional Arguments in Expression Trees

[cilerler]

What happened?

In the example below, the call to ProjectsV2(first: 10) inside the Select lambda results in this compiler error:

CS0854 - An expression tree may not contain a call or invocation that uses optional arguments.

It would be helpful to provide clearer guidance or workarounds.

var query = new Query()
                .Repository(owner: owner, name: repo)
                .Issue(number: issueNumber)
                .Select(i => new
		                {
			          i.Id,
			          i.Title,
			          i.Number,
			          Projects = i.ProjectsV2(first: 10).Nodes        // <=== CS0854
			            .Select(p => new
			              {
				              p.Number,
				              p.Title
			              })
		                });

Versions

Nuget: Octokit.GraphQL 0.40.0-beta

Relevant log output

No response

Code of Conduct

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[github-actions]

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[cilerler]

I came across this note in the Octokit GraphQL .NET documentation:

You can see a bunch of null parameters in the r.Issues() call. This is because expressions in C# do not support default parameter values, so all the unused values need to be supplied an explicit null. It sucks.

Based on this explanation, I updated my query from

Projects = i.ProjectsV2(first: 10).Nodes

to

Projects = i.ProjectsV2(10, null, null, null, null, null).Nodes

and it worked.

Leaving this workaround here in case someone else encounters the same issue.

However, I’m keeping this issue open because it highlights a need for refactoring and improved implementation/documentation to handle such cases more gracefully.