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Which functions takes a "values" parameter? I would guess it's Columns.AddRange()?
If so, then my first guess would be that the problem is with obj.GetType().GetGenericArguments() not having any items (length == 0).
I guess this is one of the reasons we try to write readable code... so we also get more specific error messages. This one-liner nonsense is bad for everyone.
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The underlying issue is that this garbage is a "one-liner". One-liners are darn near impossible to debug. LinQ invites, and even encourages this crap into the code.
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As does SQL. If a given statement works, just keep piling on until it doesn't, then post it in Q&A.
It was only in wine that he laid down no limit for himself, but he did not allow himself to be confused by it.
― Confucian Analects: Rules of Confucius about his food
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And Linq combined with extension methods makes one-liners even more fun! I write them frequently! 
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I find that adding line breaks makes it a lot easier to read. Remember, you are writing for the next person to touch the code, not the computer. It is missing some Elvis operators, before the Where, the Select, and the ToArray, along with providing a value if the null propagates to the end.
Also, you don't need the ToArray() as AddRange takes an IEnumerable<T>.
Columns
.AddRange(
obj.GetType()
.GetGenericArguments()
.FirstOrDefault()?.GetProperties()
?.Where(p =>
{
return p.GetCustomAttributes(true)
.OfType<BrowsableAttribute>()
.FirstOrDefault()?.Browsable ?? DefaultBrowsableState;
})
?.Select(p =>
{
return new ColumnHeader()
{
Name = p.Name,
Text = p.GetCustomAttributes(true)
.OfType<DisplayNameAttribute>().FirstOrDefault()?.DisplayName ?? p.Name
};
})
?? Array.Empty<ColumnHeader>()
);
"Time flies like an arrow. Fruit flies like a banana."
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In my defense I didn't write that, nor run it through autoformat yet.
Real programmers use butterflies
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Matthew Dennis wrote: I find that adding line breaks makes it a lot easier to read
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Matthew Dennis wrote: It is missing some Elvis operators
It's not. If the FirstOrDefault returns null, the GetProperties and subsequent calls won't execute. If it returns non-null, GetProperties will never return null:
Returns
An array of PropertyInfo objects representing all public properties of the current Type.
-or-
An empty array of type PropertyInfo, if the current Type does not have public properties.
Similarly, Where will never return null. If the input sequence is null, it will throw an exception. If the input sequence is empty, or there are no matching elements, it will return an empty sequence.
And the same applies to Select - it will either throw an exception, or return a non-null sequence.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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actually that is incorrect. Only the chain of conditional operators is short circuited so if you have the expression
A()?.Bb()?.C().D()
and A() returns null the B and C will not be executed but there will be an attempt to execute D on a null object.
Its sort of like async. You need to go all the way down.
[Member access operators and expressions - C# reference | Microsoft Docs](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/member-access-operators#null-conditional-operators--and-)
"Time flies like an arrow. Fruit flies like a banana."
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I'm not convinced. 
static Foo A() => null;
public class Foo
{
public Foo B() => null;
public Foo C() => null;
public Foo D() => null;
}
...
Foo result = A()?.B().C().D(); Null conditional operator | C# Online Compiler | .NET Fiddle[^]
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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You may be correct. The documentation is a little vague on the extent of the short circuiting.
"Time flies like an arrow. Fruit flies like a banana."
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I checked this out and it appears that as long as the null occurs before a ?. or ?[] operator, the rest of the chain is short circuited and has a value of NULL.
You learn something everyday.
Thanks
"Time flies like an arrow. Fruit flies like a banana."
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I'm not an expert or even a novice ...
(serious)
Can't you just "unLINQ" this and find and fix the error and LINQ it up again ?
I'd rather be phishing!
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Yes. But that's my point. To get a reasonable error message out of LINQ the solution is do it without LINQ. meh.
Real programmers use butterflies
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It's not really LINQ's fault, it's the chaining of multiple commands into a single statement and also a little of your own inexperience; given that error message many would know exactly where to look.
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A couple of possibly interesting bits of feedback, assuming that code comes from here:
- Adding it to a WinForms app created with .NET Core 3.1 or .NET 5 and turning on nullable reference types finds 17 potential accidental nulls in the code from that SO post. But the Columns.AddRange call itself isn't one of them because WinForms wasn't built with NRT enabled. So the compiler decides it can't say one way or another if passing a null values argument to AddRange is okay.
- Resharper catches the potential error whether you're using .NET Core/.NET 5 or .NET Framework. It even suggests a fix. The static analysis it's doing must look at AddRange and notice that the first thing that method does is throw an exception if values is null.
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Ryan Peden wrote: Resharper catches the potential error
Ryan Peden wrote: It even suggests a fix.
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Sounds like nullable reference types is reason enough in itself to upgrade to .Net 5.
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Ryan Peden wrote: The static analysis it's doing must look at AddRange and notice that the first thing that method does is throw an exception if values is null.
I suspect it's more likely that it has "external annotations" for the type in question.
External Annotations—ReSharper[^]
R# is already slow enough; if it had to do static analysis on every framework method you called, it would be completely unusable.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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That certainly makes using LINQ a bit nicer.
Real programmers use butterflies
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The main challenge of LINQ that you don't like (I believe) is one that is quite difficult to accept (for me too) and for many of us who originally learned imperative programming.
The main challenge is that LINQ is a declarative construct within an imperative programming language.
You probably know this already.
Declarative languages expect you to tell them what you want (not how they should do it).
However, how they actually get you want you want is hidden (black box).
So when they fail, it is quite difficult to know where / why they failed.
With imperative programming you have written the steps to get the thing to do the thing and you know where the problem is.
Squirrel From A Different Dimension
This may not help but it'll help you understand that even though the animal you are wrestling with looks very much like a normal squirrel, it is actually a squirrel that lives in another dimension and it behaves quite differently.
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p.GetCustomAttributes(true).OfType<DisplayNameAttribute>()
I believe OfType<>() is returning a null.
honey the codewitch wrote: The LINQ isn't really that bad here.
Actually, it's rather horrific. Not to mention what looks like completely unnecessary and probably wrong FirstOrDefault() usage, the reflection usage which looks like it could be simplified, and other confusing things. And the probably useless ToArray().
honey the codewitch wrote: even though I didn't write it
Whew! 
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Marc Clifton wrote: I believe OfType<>() is returning a null.
Nope.
OfType<T> will throw an exception if the input sequence is null. If the input sequence is empty, or doesn't contain any matching elements, it will return an empty sequence. It can never return null.
Also, the elements within the returned sequence will never be null.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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This is illustrative of the point of my OP. If the error was clearer there would have been no confusion here.
Real programmers use butterflies
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Yet another example of the school of thought that replacing if, for, and while by declarative constructs results in code that is simplicity itself to read, robust, and completely error free.
In a pig's eye.
Software Zen: delete this;
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