[release/11.0.1xx-preview2] Fix NullReferenceException when binding to Dictionary<Enum, object> with x:DataType - #34244

src\Controls\src\SourceGen\CompiledBindingMarkup.cs(496,16): error CS0037: (NETCORE_ENGINEERING_TELEMETRY=Build) Cannot convert null to 'bool' because it is a non-nullable value type

src\Controls\src\SourceGen\CompiledBindingMarkup.cs(496,16): error CS0037: (NETCORE_ENGINEERING_TELEMETRY=Build) Cannot convert null to 'bool' because it is a non-nullable value type

src\Controls\src\SourceGen\CompiledBindingMarkup.cs(496,16): error CS0037: (NETCORE_ENGINEERING_TELEMETRY=Build) Cannot convert null to 'bool' because it is a non-nullable value type

src\Controls\src\SourceGen\CompiledBindingMarkup.cs(496,16): error CS0037: (NETCORE_ENGINEERING_TELEMETRY=Build) Cannot convert null to 'bool' because it is a non-nullable value type