[Windows] Skip running tasks with no inputs

msbuild/Xamarin.Localization.MSBuild/MSBStrings.resx

@@ -1621,4 +1621,12 @@
             {2} and {3}: the different LogicalName metadata
         </comment>
     </data>
+
+    <data name="M7159" xml:space="preserve">
+        <value>Skipping {0} - {1} is empty.</value>
+        <comment>
+            {0}: the name of the MSBuild task that's being skipped (Copy, GetFullPaths, FilterStaticFrameworks, etc.).
+            {1}: the name of the property that is empty (SourceFiles, Items, FrameworkToPublish, etc.).
+        </comment>
+    </data>
 </root>

msbuild/Xamarin.MacDev.Tasks/MsBuildTasks/Copy.cs

@@ -1,18 +1,22 @@
 extern alias Microsoft_Build_Tasks_Core;
 
-using System;
-using System.IO;
 using System.Linq;
 
 using Microsoft.Build.Framework;
 
+using Xamarin.Localization.MSBuild;
 using Xamarin.Messaging.Build.Client;
 
 namespace Microsoft.Build.Tasks {
 	public class Copy : Microsoft_Build_Tasks_Core::Microsoft.Build.Tasks.Copy {
 		public string SessionId { get; set; } = string.Empty;
 		public override bool Execute ()
 		{
+			if (SourceFiles?.Any () != true) {
+				Log.LogMessage (MessageImportance.Low, MSBStrings.M7159 /* Skipping {0} - {1} is empty. */, nameof (Copy), nameof (SourceFiles));
+				return true;
+			}
+
 			if (!this.ShouldExecuteRemotely (SessionId))
 				return base.Execute ();
 

msbuild/Xamarin.MacDev.Tasks/Tasks/FilterStaticFrameworks.cs

@@ -22,6 +22,11 @@ public class FilterStaticFrameworks : XamarinTask, ITaskCallback {
 
 		public override bool Execute ()
 		{
+			if (FrameworkToPublish?.Any () != true) {
+				Log.LogMessage (MessageImportance.Low, MSBStrings.M7159 /* Skipping {0} - {1} is empty. */, nameof (FilterStaticFrameworks), nameof (FrameworkToPublish));
+				return true;
+			}
+
 			if (ShouldExecuteRemotely ())
 				return new TaskRunner (SessionId, BuildEngine4).RunAsync (this).Result;
 

msbuild/Xamarin.MacDev.Tasks/Tasks/GetFileSystemEntries.cs

@@ -43,6 +43,11 @@ public class GetFileSystemEntries : XamarinTask, ICancelableTask, ITaskCallback
 
 		public override bool Execute ()
 		{
+			if (DirectoryPath?.Any () != true) {
+				Log.LogMessage (MessageImportance.Low, MSBStrings.M7159 /* Skipping {0} - {1} is empty. */, nameof (GetFileSystemEntries), nameof (DirectoryPath));
+				return true;
+			}
+
 			if (ShouldExecuteRemotely ())
 				return new TaskRunner (SessionId, BuildEngine4).RunAsync (this).Result;
 

msbuild/Xamarin.MacDev.Tasks/Tasks/GetFullPaths.cs

@@ -6,7 +6,7 @@
 using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
 
-using Xamarin.MacDev.Tasks;
+using Xamarin.Localization.MSBuild;
 using Xamarin.Messaging.Build.Client;
 
 #nullable enable
@@ -23,6 +23,11 @@ public class GetFullPaths : XamarinTask, ICancelableTask, ITaskCallback {
 
 		public override bool Execute ()
 		{
+			if (Items?.Any () != true) {
+				Log.LogMessage (MessageImportance.Low, MSBStrings.M7159 /* Skipping {0} - {1} is empty. */, nameof (GetFullPaths), nameof (Items));
+				return true;
+			}
+
 			if (ShouldExecuteRemotely ())
 				return new TaskRunner (SessionId, BuildEngine4).RunAsync (this).Result;