Merge pull request dotnet#8671 from LWChris/patch-1

Document exceptions and alternates for Enumerable.ToHashSet

Author: tarekgh

xml/System.Linq/Enumerable.xml

@@ -13378,6 +13378,9 @@ If `count` is not a positive number, this method returns an empty enumerable col
         <summary>Creates a <see cref="T:System.Collections.Generic.HashSet`1" /> from an <see cref="T:System.Collections.Generic.IEnumerable`1" />.</summary>
         <returns>A <see cref="T:System.Collections.Generic.HashSet`1" /> that contains values of type <paramref name="TSource" /> selected from the input sequence.</returns>
         <remarks>To be added.</remarks>
+        <exception cref="T:System.ArgumentNullException">
+          <paramref name="source" /> is <see langword="null" />.</exception>
+        <altmember cref="M:System.Linq.Enumerable.ToHashSet``1(System.Collections.Generic.IEnumerable{``0},System.Collections.Generic.IEqualityComparer{``0})" />
       </Docs>
     </Member>
     <Member MemberName="ToHashSet&lt;TSource&gt;">
@@ -13423,6 +13426,9 @@ If `count` is not a positive number, this method returns an empty enumerable col
         <summary>Creates a <see cref="T:System.Collections.Generic.HashSet`1" /> from an <see cref="T:System.Collections.Generic.IEnumerable`1" /> using the <paramref name="comparer" /> to compare keys.</summary>
         <returns>A <see cref="T:System.Collections.Generic.HashSet`1" /> that contains values of type <paramref name="TSource" /> selected from the input sequence.</returns>
         <remarks>To be added.</remarks>
+        <exception cref="T:System.ArgumentNullException">
+          <paramref name="source" /> is <see langword="null" />.</exception>
+        <altmember cref="M:System.Linq.Enumerable.ToHashSet``1(System.Collections.Generic.IEnumerable{``0})" />
       </Docs>
     </Member>
     <Member MemberName="ToList&lt;TSource&gt;">