Fix build warnings

Update code samples for the template in use to remove nullable warnings.

I did this as we plan to have nullable annotations on by default in this version of the spec.

Author: BillWagner

standard/classes.md

@@ -878,7 +878,7 @@ All members of a generic class can use type parameters from any enclosing class,
 > class C<V>
 > {
 >     public V f1;
->     public C<V> f2 = null;
+>     public C<V> f2 = null!;
 >
 >     public C(V x)
 >     {
@@ -2390,7 +2390,7 @@ When performing overload resolution, a method with a parameter array might be ap
 > ```csharp
 > class Test
 > {
->     static void F(params string[] array) =>
+>     static void F(params string?[]? array) =>
 >         Console.WriteLine(array == null);
 > 
 >     static void Main()
@@ -5136,7 +5136,7 @@ Finalizers are invoked automatically, and cannot be invoked explicitly. An insta
 > {
 >     static void Main()
 >     {
->         B b = new B();
+>         B? b = new B();
 >         b = null;
 >         GC.Collect();
 >         GC.WaitForPendingFinalizers();

standard/delegates.md

@@ -291,22 +291,22 @@ Attempting to invoke a delegate instance whose value is `null` results in an exc
 >         cd1(-1);             // call M1
 >         D cd2 = new D(C.M2);
 >         cd2(-2);             // call M2
->         D cd3 = cd1 + cd2;
+>         D? cd3 = cd1 + cd2;
 >         cd3(10);             // call M1 then M2
 >         cd3 += cd1;
 >         cd3(20);             // call M1, M2, then M1
 >         C c = new C();
 >         D cd4 = new D(c.M3);
 >         cd3 += cd4;
->         cd3(30);             // call M1, M2, M1, then M3
+>         cd3!(30);             // call M1, M2, M1, then M3
 >         cd3 -= cd1;          // remove last M1
->         cd3(40);             // call M1, M2, then M3
+>         cd3!(40);             // call M1, M2, then M3
 >         cd3 -= cd4;
->         cd3(50);             // call M1 then M2
+>         cd3!(50);             // call M1 then M2
 >         cd3 -= cd2;
->         cd3(60);             // call M1
+>         cd3!(60);             // call M1
 >         cd3 -= cd2;          // impossible removal is benign
->         cd3(60);             // call M1
+>         cd3!(60);             // call M1
 >         cd3 -= cd1;          // invocation list is empty so cd3 is null
 >         // cd3(70);          // System.NullReferenceException thrown
 >         cd3 -= cd1;          // impossible removal is benign

standard/expressions.md

@@ -3218,7 +3218,7 @@ Except for the `stackalloc` operator, C# provides no predefined constructs for m
 > 
 > public class Widget<T>
 > {
->     public static implicit operator Widget<T>(Span<double> sp) { return null; }
+>     public static implicit operator Widget<T>(Span<double> sp) { return null!; }
 > }
 > ```
 >
@@ -3800,7 +3800,7 @@ The predefined addition operators are listed below. For numeric and enumeration
   > {
   >     static void Main()
   >     {
-  >         string s = null;
+  >         string? s = null;
   >         Console.WriteLine("s = >" + s + "<");  // Displays s = ><
   >
   >         int i = 1;
@@ -6389,8 +6389,8 @@ The run-time processing of a simple assignment of the form `x = y` with type `T`
 >
 > <!-- Example: {template:"standalone-console", name:"SimpleAssignment1", expectedException:"ArrayTypeMismatchException"} -->
 > ```csharp
-> string[] sa = new string[10];
-> object[] oa = sa;
+> string?[] sa = new string[10];
+> object?[] oa = sa;
 > oa[0] = null;              // OK
 > oa[1] = "Hello";           // OK
 > oa[2] = new ArrayList();   // ArrayTypeMismatchException

standard/statements.md

@@ -1926,7 +1926,7 @@ using (ResourceType rN = eN)
 >         }
 >         using (TextReader r = File.OpenText("log.txt"))
 >         {
->             string s;
+>             string? s;
 >             while ((s = r.ReadLine()) != null)
 >             {
 >                 Console.WriteLine(s);

tools/example-templates/additional-files/HelpAttribute.cs

@@ -10,7 +10,7 @@ public string Topic
     { 
         get;
         set;
-    }
+    } = null!;
 
-    public string Url { get; }
+    public string Url { get; } = null!;
 }