fix: null source raises ArgumentNullException for insertAt, removeAt, updateAt

Previously, passing null to TaskSeq.insertAt, insertManyAt, removeAt,
removeManyAt, and updateAt would throw a NullReferenceException from deep
within the taskSeq builder, inconsistent with every other function in the
library which eagerly raises ArgumentNullException via checkNonNull.

- Add checkNonNull (nameof source) source to insertAt, removeAt, removeManyAt, updateAt
- Add checkNonNull "values" values to insertAt when called with Many (insertManyAt)
- Add null-source tests to TaskSeq.InsertAt, RemoveAt, UpdateAt test files
- 5017 tests pass (4 new null-arg tests added)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

release-notes.txt

@@ -2,6 +2,7 @@
 Release notes:
 
 1.0.0
+    - fixes: TaskSeq.insertAt, insertManyAt, removeAt, removeManyAt, updateAt now raise ArgumentNullException (not NullReferenceException) when given a null source; insertManyAt also validates the values argument
     - refactor: simplify lengthBy and lengthBeforeMax to use while! and remove the redundant mutable 'go' and initial MoveNextAsync
     - adds TaskSeq.distinctUntilChangedWith and TaskSeq.distinctUntilChangedWithAsync, #345
     - adds TaskSeq.withCancellation, #167

src/FSharp.Control.TaskSeq.Test/TaskSeq.InsertAt.Tests.fs

@@ -16,6 +16,18 @@ open FSharp.Control
 exception SideEffectPastEnd of string
 
 module EmptySeq =
+    [<Fact>]
+    let ``Null source is invalid`` () =
+        assertNullArg <| fun () -> TaskSeq.insertAt 0 99 null
+
+        assertNullArg
+        <| fun () -> TaskSeq.insertManyAt 0 TaskSeq.empty null
+
+    [<Fact>]
+    let ``Null values argument is invalid for insertManyAt`` () =
+        assertNullArg
+        <| fun () -> TaskSeq.insertManyAt 0 null (TaskSeq.ofList [ 1 ])
+
     [<Theory; ClassData(typeof<TestEmptyVariants>)>]
     let ``TaskSeq-insertAt(0) on empty input returns singleton`` variant =
         Gen.getEmptyVariant variant

src/FSharp.Control.TaskSeq.Test/TaskSeq.RemoveAt.Tests.fs

@@ -16,6 +16,12 @@ open FSharp.Control
 exception SideEffectPastEnd of string
 
 module EmptySeq =
+    [<Fact>]
+    let ``Null source is invalid`` () =
+        assertNullArg <| fun () -> TaskSeq.removeAt 0 null
+
+        assertNullArg <| fun () -> TaskSeq.removeManyAt 0 1 null
+
     [<Theory; ClassData(typeof<TestEmptyVariants>)>]
     let ``TaskSeq-removeAt(0) on empty input raises`` variant =
         fun () ->

src/FSharp.Control.TaskSeq.Test/TaskSeq.UpdateAt.Tests.fs

@@ -15,6 +15,9 @@ open FSharp.Control
 exception SideEffectPastEnd of string
 
 module EmptySeq =
+    [<Fact>]
+    let ``Null source is invalid`` () = assertNullArg <| fun () -> TaskSeq.updateAt 0 99 null
+
     [<Theory; ClassData(typeof<TestEmptyVariants>)>]
     let ``TaskSeq-updateAt(0) on empty input should throw ArgumentException`` variant =
         fun () ->

src/FSharp.Control.TaskSeq/TaskSeqInternal.fs

@@ -1369,6 +1369,12 @@ module internal TaskSeqInternal =
 
     /// InsertAt or InsertManyAt
     let insertAt index valueOrValues (source: TaskSeq<_>) =
+        checkNonNull (nameof source) source
+
+        match valueOrValues with
+        | Many values -> checkNonNull "values" values
+        | One _ -> ()
+
         raiseCannotBeNegative (nameof index) index
 
         taskSeq {
@@ -1394,6 +1400,7 @@ module internal TaskSeqInternal =
         }
 
     let removeAt index (source: TaskSeq<'T>) =
+        checkNonNull (nameof source) source
         raiseCannotBeNegative (nameof index) index
 
         taskSeq {
@@ -1411,6 +1418,7 @@ module internal TaskSeqInternal =
         }
 
     let removeManyAt index count (source: TaskSeq<'T>) =
+        checkNonNull (nameof source) source
         raiseCannotBeNegative (nameof index) index
 
         taskSeq {
@@ -1429,6 +1437,7 @@ module internal TaskSeqInternal =
         }
 
     let updateAt index value (source: TaskSeq<'T>) =
+        checkNonNull (nameof source) source
         raiseCannotBeNegative (nameof index) index
 
         taskSeq {