The execution of "Execute function now..." is failed with an error when entering blank request body for .NET 3.1 C# project

[v-mengwe]

OS: Win10 Build Version: 20211206.2 Regression: Not a regression

Repro Steps:

1. Open an empty folder in VS Code -> Create a new .NET 3.1 C# project with HTTPTrigger template.
2. Debug -> Navigate to Azure view -> Expand the Functions node of "Local Project" -> Right click the function and execute "Execute Function Now..." -> Enter blank when asked to enter request body.
3. Check whether the execution of "Execute Function Now..." is successful without any error.

Expect: The execution of "Execute function now..." is successful without any error.

Actual: The execution of "Execute function now..." is failed with an error.

More Info:

1. This issue doesn't reproduce for JavaScript/TypeScript/PowerShell/.NET 5/Java project.
2. This issue also reproduces for Python/.NET 6 project.