Update live with current master

CONTRIBUTING.md

@@ -2,6 +2,9 @@
 
 Thank you for your interest in contributing to the .NET documentation!
 
+> We're in the process of moving our guidelines into a site-wide contribution guide. 
+> To see the new guidance, visit [Microsoft Docs contributor guide overview](https://docs.microsoft.com/contribute/).
+
 The document covers the process for contributing to the articles and code samples that are hosted on the [.NET documentation site](https://docs.microsoft.com/dotnet). Contributions may be as simple as typo corrections or as complex as new articles.
 
 * [Process for contributing](#process-for-contributing)

docs/csharp/programming-guide/events/codesnippet/CSharp/how-to-implement-interface-events_1.cs

@@ -74,19 +74,12 @@ event EventHandler IShape.OnDraw
         public void Draw()
         {
             // Raise IDrawingObject's event before the object is drawn.
-            EventHandler handler = PreDrawEvent;
-            if (handler != null)
-            {
-                handler(this, new EventArgs());
-            }
+            PreDrawEvent?.Invoke(this, EventArgs.Empty);
+
             Console.WriteLine("Drawing a shape.");
 
-            // RaiseIShape's event after the object is drawn.
-            handler = PostDrawEvent;
-            if (handler != null)
-            {
-                handler(this, new EventArgs());
-            }
+            // Raise IShape's event after the object is drawn.
+            PostDrawEvent?.Invoke(this, EventArgs.Empty);
         }
     }
     public class Subscriber1
@@ -95,7 +88,7 @@ public class Subscriber1
         public Subscriber1(Shape shape)
         {
             IDrawingObject d = (IDrawingObject)shape;
-            d.OnDraw += new EventHandler(d_OnDraw);
+            d.OnDraw += d_OnDraw;
         }
 
         void d_OnDraw(object sender, EventArgs e)
@@ -109,7 +102,7 @@ public class Subscriber2
         public Subscriber2(Shape shape)
         {
             IShape d = (IShape)shape;
-            d.OnDraw += new EventHandler(d_OnDraw);
+            d.OnDraw += d_OnDraw;
         }
 
         void d_OnDraw(object sender, EventArgs e)
@@ -139,4 +132,4 @@ static void Main(string[] args)
     Sub1 receives the IDrawingObject event.
     Drawing a shape.
     Sub2 receives the IShape event.
-*/
+*/

docs/csharp/programming-guide/events/how-to-implement-interface-events.md

@@ -37,20 +37,17 @@ An [interface](../../../csharp/language-reference/keywords/interface.md) can dec
             }  
             protected virtual void OnShapeChanged(MyEventArgs e)  
             {  
-                if(ShapeChanged != null)  
-                {  
-                   ShapeChanged(this, e);  
-                }  
+                ShapeChanged?.Invoke(this, e);  
             }  
         }  
 
     }  
     ```  
 
 ## Example  
- The following example shows how to handle the less-common situation in which your class inherits from two or more interfaces and each interface has an event with the same name. In this situation, you must provide an explicit interface implementation for at least one of the events. When you write an explicit interface implementation for an event, you must also write the `add` and `remove` event accessors. Normally these are provided by the compiler, but in this case the compiler cannot provide them.  
+The following example shows how to handle the less-common situation in which your class inherits from two or more interfaces and each interface has an event with the same name. In this situation, you must provide an explicit interface implementation for at least one of the events. When you write an explicit interface implementation for an event, you must also write the `add` and `remove` event accessors. Normally these are provided by the compiler, but in this case the compiler cannot provide them.  
 
- By providing your own accessors, you can specify whether the two events are represented by the same event in your class, or by different events. For example, if the events should be raised at different times according to the interface specifications, you can associate each event with a separate implementation in your class. In the following example, subscribers determine which `OnDraw` event they will receive by casting the shape reference to either an `IShape` or an `IDrawingObject`.  
+By providing your own accessors, you can specify whether the two events are represented by the same event in your class, or by different events. For example, if the events should be raised at different times according to the interface specifications, you can associate each event with a separate implementation in your class. In the following example, subscribers determine which `OnDraw` event they will receive by casting the shape reference to either an `IShape` or an `IDrawingObject`.  
 
  [!code-csharp[csProgGuideEvents#10](../../../csharp/programming-guide/events/codesnippet/CSharp/how-to-implement-interface-events_1.cs)]  
 

docs/csharp/tuples.md

@@ -153,7 +153,8 @@ Beginning with C# 7.3, tuple types support the `==` and `!=` operators. These op
 
 [!code-csharp[TupleEquality](../../samples/snippets/csharp/tuples/tuples/program.cs#Equality "Testing tuples for equality")]
 
-There are several rules that make tuple equality tests more convenient. Tuple equality performs [lifted conversions](/dotnet/csharp/language-reference/language-specification/conversions.md#lifted-conversion-operators) if one of the tuples is a nullable tuple, as shown in the following code:
+There are several rules that make tuple equality tests more convenient. Tuple equality performs [lifted conversions](/dotnet/csharp/language-reference/language-specification/conversions#lifted-conversion-operators) if one of the tuples is a nullable tuple, as shown in the following code:
+
 
 [!code-csharp[NullableTupleEquality](../../samples/snippets/csharp/tuples/tuples/program.cs#NullableEquality "Comparing Tuples and nullable tuples")]