fix #2210

Author: jonsequitur

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

@@ -8,6 +8,7 @@
 using System.IO;
 using System.Linq;
 using System.Net;
+using System.Threading;
 using Xunit;
 
 namespace System.CommandLine.Tests.Binding
@@ -195,6 +196,30 @@ public void Bool_parses_as_true_when_the_option_has_been_applied(string commandL
                 .BeTrue();
         }
 
+        [Fact] // https://github.com/dotnet/command-line-api/issues/2210
+        public void Nullable_bool_with_unparseable_argument_does_not_throw()
+        {
+            CliRootCommand rootCommand = new();
+            CliOption<bool?> option = new("--test");
+            rootCommand.Options.Add(option);
+            var result = rootCommand.Parse("--test ouch");
+
+            result.Invoking(r =>  r.GetValue(option))
+                  .Should().NotThrow();
+        }
+
+        [Fact] // https://github.com/dotnet/command-line-api/issues/2210
+        public void Bool_with_unparseable_argument_does_not_throw()
+        {
+            CliRootCommand rootCommand = new();
+            CliOption<bool> option = new("--test");
+            rootCommand.Options.Add(option);
+            var result = rootCommand.Parse("--test ouch");
+
+            result.Invoking(r => r.GetValue(option))
+                  .Should().NotThrow();
+        }
+
         [Theory]
         [InlineData("the-command -x")]
         [InlineData("the-command -x true")]

src/System.CommandLine/Parsing/ParseOperation.cs

@@ -246,9 +246,10 @@ private void ParseOptionArguments(OptionResult optionResult)
                         break;
                     }
                 }
-                else if (argument.ValueType == typeof(bool) && 
+                else if ((argument.ValueType == typeof(bool) || argument.ValueType == typeof(bool?))  && 
                          !bool.TryParse(CurrentToken.Value, out _))
                 {
+                    // Don't greedily consume the following token for bool. The presence of the option token (i.e. a flag) is sufficient.
                     break;
                 }