An unhandled exception occurred while processing the request: FormatException: The header contains invalid values at index 0

Question: An unhandled exception occurred while processing the request: FormatException: The header contains invalid values at index 0: '<null>'
Why am I receiving this error in MVC AspNet 6 using Visual Studio 2022?


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Answer: This error seems to be the result of passing a null contentType (content-type) in a PhysicalFile() function. The PhysicalFile() function does not determine what content type it is to return to the caller. Make sure that the content type is actually valid before returning to the Function Caller.


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