changed some error message and cleaned up code

src/Workspaces/Core/Portable/CodeGeneration/AbstractCodeGenerationService.cs

@@ -98,14 +98,14 @@ protected static T Cast<T>(object value)
         {
             if (destination == null)
             {
-                throw new ArgumentNullException("destination");
+                throw new ArgumentNullException(nameof(destination));
             }
 
             if (!(destination is TDeclarationNode))
             {
                 throw new ArgumentException(
                     string.Format(WorkspacesResources.InvalidDestinationNode, typeof(TDeclarationNode).Name, destination.GetType().Name),
-                    "destination");
+                    nameof(destination));
             }
         }
 
@@ -115,7 +115,7 @@ protected static T Cast<T>(object value)
         {
             if (destination == null)
             {
-                throw new ArgumentNullException("destination");
+                throw new ArgumentNullException(nameof(destination));
             }
 
             if (!(destination is TDeclarationNode1) &&
@@ -124,7 +124,7 @@ protected static T Cast<T>(object value)
                 throw new ArgumentException(
                     string.Format(WorkspacesResources.InvalidDestinationNode2,
                         typeof(TDeclarationNode1).Name, typeof(TDeclarationNode2).Name, destination.GetType().Name),
-                    "destination");
+                    nameof(destination));
             }
         }
 
@@ -135,7 +135,7 @@ protected static T Cast<T>(object value)
         {
             if (destination == null)
             {
-                throw new ArgumentNullException("destination");
+                throw new ArgumentNullException(nameof(destination));
             }
 
             if (!(destination is TDeclarationNode1) &&
@@ -145,7 +145,7 @@ protected static T Cast<T>(object value)
                 throw new ArgumentException(
                     string.Format(WorkspacesResources.InvalidDestinationNode3,
                         typeof(TDeclarationNode1).Name, typeof(TDeclarationNode2).Name, typeof(TDeclarationNode3).Name, destination.GetType().Name),
-                    "destination");
+                    nameof(destination));
             }
         }
 
@@ -163,7 +163,7 @@ protected static T Cast<T>(object value)
                 throw new ArgumentException(
                     string.Format(WorkspacesResources.InvalidDestinationNode3,
                         typeof(TDeclarationNode1).Name, typeof(TDeclarationNode2).Name, typeof(TDeclarationNode3).Name, typeof(TDeclarationNode4).Name),
-                    "destination");
+                    nameof(destination));
             }
         }
 

src/Workspaces/Core/Portable/WorkspacesResources.Designer.cs

@@ -467,7 +467,7 @@ internal class WorkspacesResources {
         }
         
         /// <summary>
-        ///   Looks up a localized string similar to Destination type must be a {0}. but given one is {1}..
+        ///   Looks up a localized string similar to Destination type must be a {0}, but given one is {1}..
         /// </summary>
         internal static string InvalidDestinationNode {
             get {
@@ -476,7 +476,7 @@ internal class WorkspacesResources {
         }
         
         /// <summary>
-        ///   Looks up a localized string similar to Destination type must be a {0} or a {1}. but given one is {2}..
+        ///   Looks up a localized string similar to Destination type must be a {0} or a {1}, but given one is {2}..
         /// </summary>
         internal static string InvalidDestinationNode2 {
             get {
@@ -485,7 +485,7 @@ internal class WorkspacesResources {
         }
         
         /// <summary>
-        ///   Looks up a localized string similar to Destination type must be a {0}, {1} or {2}. but given one is {3}..
+        ///   Looks up a localized string similar to Destination type must be a {0}, {1} or {2}, but given one is {3}..
         /// </summary>
         internal static string InvalidDestinationNode3 {
             get {

src/Workspaces/Core/Portable/WorkspacesResources.resx

@@ -130,13 +130,13 @@
     <value>Cycle detected in extensions</value>
   </data>
   <data name="InvalidDestinationNode" xml:space="preserve">
-    <value>Destination type must be a {0}. but given one is {1}.</value>
+    <value>Destination type must be a {0}, but given one is {1}.</value>
   </data>
   <data name="InvalidDestinationNode2" xml:space="preserve">
-    <value>Destination type must be a {0} or a {1}. but given one is {2}.</value>
+    <value>Destination type must be a {0} or a {1}, but given one is {2}.</value>
   </data>
   <data name="InvalidDestinationNode3" xml:space="preserve">
-    <value>Destination type must be a {0}, {1} or {2}. but given one is {3}.</value>
+    <value>Destination type must be a {0}, {1} or {2}, but given one is {3}.</value>
   </data>
   <data name="CouldNotFindLocationToGen" xml:space="preserve">
     <value>Could not find location to generation symbol into.</value>