Remove not null constraint, define nullArgCheck and Unchecked.nonNull

Author: gusty

src/FSharpPlus/Extensions/Array.fs

@@ -8,6 +8,7 @@ module Array =
 
     open System
     open FSharp.Core.CompilerServices
+    open FSharpPlus.Internals.Errors
 
     /// <summary>Adds an element to the beginning of the given array</summary>
     /// <param name="value">The element to add</param>

src/FSharpPlus/Extensions/Dict.fs

@@ -15,7 +15,7 @@ module Dict =
 
     /// <summary>Creates an empty dictionary.</summary>
     [<GeneralizableValue>]
-    let empty<'Key, 'U when 'Key : equality and 'Key : not null> = printfn "creating"; Dictionary<'Key, 'U> () :> IDictionary<_,_>
+    let empty<'Key, 'U when 'Key : equality> = printfn "creating"; Dictionary<'Key, 'U> () :> IDictionary<_,_>
 
     /// <summary>Tries to get the value of the given key.</summary>
     /// <remarks>This is a function wrapper for the IDictionary.TryGetValue method,

src/FSharpPlus/Extensions/Dictionary.fs

@@ -16,7 +16,7 @@ module Dictionary =
 
     /// <summary>Creates an empty dictionary.</summary>
     [<GeneralizableValue>]
-    let empty<'Key, 'U when 'Key : equality and 'Key : not null> = Dictionary<'Key, 'U> ()
+    let empty<'Key, 'U when 'Key : equality> = Dictionary<'Key, 'U> ()
 
     /// <summary>Tries to get the value of the given key.</summary>
     /// <remarks>Note: this is a function wrapper for the Dictionary.TryGetValue method,

src/FSharpPlus/Extensions/Exception.fs

@@ -5,6 +5,7 @@
 module Exception =
     open System
     open System.Runtime.ExceptionServices
+    open FSharpPlus.Internals.Errors
 
     #if !FABLE_COMPILER
 

src/FSharpPlus/Extensions/Extensions.fs

@@ -4,6 +4,7 @@ namespace FSharpPlus
 module Extensions =
 
     open System
+    open FSharpPlus.Internals.Errors
 
     type Collections.Generic.IEnumerable<'T> with
         member this.GetSlice = function

src/FSharpPlus/Extensions/HashSet.fs

@@ -4,6 +4,7 @@
 [<RequireQualifiedAccess>]
 module HashSet =
     open System.Collections.Generic
+    open FSharpPlus.Internals.Errors
 
     /// <summary>The empty set for the type 'T.</summary>
     [<GeneralizableValue>]

src/FSharpPlus/Extensions/IReadOnlyDictionary.fs

@@ -12,7 +12,7 @@ module IReadOnlyDictionary =
 
     /// <summary>Creates an empty read-only dictionary.</summary>
     [<GeneralizableValue>]
-    let empty<'Key, 'U when 'Key : equality and 'Key : not null> = Dictionary<'Key, 'U> () :> IReadOnlyDictionary<_,_>
+    let empty<'Key, 'U when 'Key : equality> = Dictionary<'Key, 'U> () :> IReadOnlyDictionary<_,_>
 
     /// Replaces or sets the item associated with a specified key with the specified value.
     let add key value (source: IReadOnlyDictionary<'Key, 'Value>) = source |> Seq.map (|KeyValue|) |> Map |> Map.add key value :> IReadOnlyDictionary<_,_>

src/FSharpPlus/Extensions/List.fs

@@ -8,6 +8,7 @@ module List =
 
     open System
     open FSharp.Core.CompilerServices
+    open FSharpPlus.Internals.Errors
 
     /// <summary>Returns a list that contains one item only.</summary>
     ///

src/FSharpPlus/Extensions/ResizeArray.fs

@@ -4,6 +4,8 @@
 [<RequireQualifiedAccess>]
 module ResizeArray =
 
+    open FSharpPlus.Internals.Errors
+
     /// <summary>Builds a new ResizeArray whose elements are the results of applying the given function
     /// to each of the elements of the ResizeArray.</summary>
     ///

src/FSharpPlus/Extensions/Seq.fs

@@ -4,6 +4,7 @@ namespace FSharpPlus
 [<RequireQualifiedAccess>]
 module Seq =
     open System
+    open FSharpPlus.Internals.Errors
 
     /// <summary>Adds an element to the beginning of the given sequence</summary>
     /// <param name="value">The element to add</param>