Is there an existing issue for this?
Describe the bug
Consider the following code:
string value = string.Join("\n", Request.Headers["NonExistentHeader"]);It causes the following exception in runtime at method string.Join(string separator, string[] value):
ArgumentNullException: Value cannot be null. (Parameter 'value')
For a very strange reason, the implicit cast of an empty StringValues struct to string[] type returns null:
string[] arr = default(StringValues);
Console.WriteLine("string[] is null: {0}", arr is null); // prints 'string[] is null: True' messageWhile a similar cast to IEnumerable returns an expected non-null value:
var seq = (IEnumerable<string>)default(StringValues);
Console.WriteLine("IEnumerable<string> is null: {0}", seq is null); // prints 'IEnumerable<string> is null: False' messageWhen C# compiler compiles string.Join("\n", Request.Headers["NonExistentHeader"]) expression, it selects string.Join(string separator, string[] value) overload and this makes the expression to crash at runtime. While the project has nullable checks enabled, C# compiler is not able to catch that null reference error at compile time.
It looks like a bug because structs are never expected to be null and thus their cast operators should avoid producing null values as well, unless there is a very good reason for that.
The following approach allows to workaround the issue:
string value = string.Join("\n", (IEnumerable<string>)Request.Headers["NonExistentHeader"]);It would be nice to have a consistent behavior here (non-null string[] is expected and preferred). But even if there is a null then C# compiler should be able to catch it at compile time.
Expected Behavior
(string[])default(StringValues) aways returns a non-null value.
Steps To Reproduce
string value = string.Join("\n", Request.Headers["NonExistentHeader"]);Exceptions (if any)
ArgumentNullException: Value cannot be null. (Parameter 'value')
at string.Join(string separator, string[] value)
.NET Version
6.0.401
Anything else?
Server: Kestrel
Is there an existing issue for this?
Describe the bug
Consider the following code:
It causes the following exception in runtime at method
string.Join(string separator, string[] value):ArgumentNullException: Value cannot be null. (Parameter 'value')For a very strange reason, the implicit cast of an empty
StringValuesstruct tostring[]type returnsnull:While a similar cast to IEnumerable returns an expected non-null value:
When C# compiler compiles
string.Join("\n", Request.Headers["NonExistentHeader"])expression, it selectsstring.Join(string separator, string[] value)overload and this makes the expression to crash at runtime. While the project has nullable checks enabled, C# compiler is not able to catch that null reference error at compile time.It looks like a bug because structs are never expected to be
nulland thus their cast operators should avoid producingnullvalues as well, unless there is a very good reason for that.The following approach allows to workaround the issue:
It would be nice to have a consistent behavior here (non-null
string[]is expected and preferred). But even if there is anullthen C# compiler should be able to catch it at compile time.Expected Behavior
(string[])default(StringValues)aways returns a non-null value.Steps To Reproduce
Exceptions (if any)
ArgumentNullException: Value cannot be null. (Parameter 'value')
at string.Join(string separator, string[] value)
.NET Version
6.0.401
Anything else?
Server: Kestrel