fix #1623

Author: jonsequitur

src/System.CommandLine.Tests/Binding/TypeConversionTests.cs

@@ -633,6 +633,28 @@ public void Values_can_be_correctly_converted_to_nullable_float_without_the_pars
             value.Should().Be(123.456f);
         }
 
+        [Fact]
+        public void Values_can_be_correctly_converted_to_Guid_without_the_parser_specifying_a_custom_converter()
+        {
+            var guidString = "75517282-018F-46BB-B15F-1D8DBFE23F6E";
+            var option = new Option<Guid>("-x");
+
+            var value = option.Parse($"-x {guidString}").GetValueForOption(option);
+
+            value.Should().Be(Guid.Parse(guidString));
+        }
+        
+        [Fact]
+        public void Values_can_be_correctly_converted_to_nullable_Guid_without_the_parser_specifying_a_custom_converter()
+        {
+            var guidString = "75517282-018F-46BB-B15F-1D8DBFE23F6E";
+            var option = new Option<Guid?>("-x");
+
+            var value = option.Parse($"-x {guidString}").GetValueForOption(option);
+
+            value.Should().Be(Guid.Parse(guidString));
+        }
+
         [Fact]
         public void Values_can_be_correctly_converted_to_Uri_without_the_parser_specifying_a_custom_converter()
         {

src/System.CommandLine/Binding/ArgumentConverter.StringConverters.cs

@@ -112,6 +112,18 @@ internal static partial class ArgumentConverter
             value = default;
             return false;
         },
+        
+        [typeof(Guid)] = (string input, out object? value) =>
+        {
+            if (Guid.TryParse(input, out var parsed))
+            {
+                value = parsed;
+                return true;
+            }
+
+            value = default;
+            return false;
+        },
 
         [typeof(int)] = (string token, out object? value) =>
         {