Nullable property always OnPropertyChanged or OnPropertyChanging

[Alexander-Bodnar]

Describe the issue

Nullable property always OnPropertyChanged or OnPropertyChanging on
Fody Version=6.6.3
PropertyChanged.Fody Version=4.0.3
PropertyChanging.Fody Version=1.30.2

but works correctly on
Fody Version=6.0.0
PropertyChanged.Fody Version=3.1.3
PropertyChanging.Fody Version=1.30.0

Minimal Repro

<PropertyGroup>
   <TargetFramework>net6.0</TargetFramework>
   <ImplicitUsings>enable</ImplicitUsings>
   <Nullable>enable</Nullable>
</PropertyGroup>
  
<ItemGroup>
  <PackageReference Include="Fody" Version="6.6.3">
    <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
    </PackageReference>
  <PackageReference Include="PropertyChanged.Fody" Version="4.0.3" />
  <PackageReference Include="PropertyChanging.Fody" Version="1.30.2" />
</ItemGroup>

Сase 1:

<Weavers xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="FodyWeavers.xsd">
  <PropertyChanging />
  <PropertyChanged />
</Weavers>

public virtual void set_Birthday(DateTime? value)
{
    if (!Nullable.Equals<DateTime>(this.Birthday, value))
    {
        this.OnPropertyChanging("Birthday");
        this.<Birthday>k__BackingField = value;
    }
    this.OnPropertyChanged("Birthday"); // <-- !!! Changed always
}

public virtual void set_Birthday2(DateTime value)
{
    if (!DateTime.Equals(this.<Birthday2>k__BackingField, value))
    {
        this.OnPropertyChanging("Birthday2");
        this.<Birthday2>k__BackingField = value;
        this.OnPropertyChanged("Birthday2");
    }
}

Сase 2: Swap PropertyChanging and PropertyChanged

<Weavers xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="FodyWeavers.xsd">
	<PropertyChanged />
	<PropertyChanging />
</Weavers>

public virtual void set_Birthday(DateTime? value)
{
    this.OnPropertyChanging("Birthday");  // <-- !!! Changing always
    if (!Nullable.Equals<DateTime>(this.Birthday, value))
    {
        this.<Birthday>k__BackingField = value;
        this.OnPropertyChanged("Birthday");
    }
}

public virtual void set_Birthday2(DateTime value)
{
    if (!DateTime.Equals(this.<Birthday2>k__BackingField, value))
    {
        this.OnPropertyChanging("Birthday2");
        this.<Birthday2>k__BackingField = value;
        this.OnPropertyChanged("Birthday2");
    }
}

[ltrzesniewski]

I can repro this:

[ImplementPropertyChanging]
[AddINotifyPropertyChangedInterface]
public class Test
{
    public DateTime Foo { get; set; }
    public DateTime? Bar { get; set; }
}

.method public hidebysig specialname 
	instance void set_Foo (
		valuetype [System.Runtime]System.DateTime 'value'
	) cil managed 
{
	.custom instance void [System.Runtime]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
		01 00 00 00
	)
	.maxstack 2

	IL_0000: ldarg.0
	IL_0001: ldfld     valuetype [System.Runtime]System.DateTime FodyTemp.Test::'<Foo>k__BackingField'
	IL_0006: ldarg.1
	IL_0007: call      bool [System.Runtime]System.DateTime::Equals(valuetype [System.Runtime]System.DateTime, valuetype [System.Runtime]System.DateTime)
	IL_000C: brfalse.s IL_0010

	IL_000E: br.s      IL_002E

	IL_0010: nop
	IL_0011: ldarg.0
	IL_0012: ldstr     "Foo"
	IL_0017: callvirt  instance void FodyTemp.Test::OnPropertyChanging(string)
	IL_001C: ldarg.0
	IL_001D: ldarg.1
	IL_001E: stfld     valuetype [System.Runtime]System.DateTime FodyTemp.Test::'<Foo>k__BackingField'
	IL_0023: ldarg.0
	IL_0024: ldsfld    class [System.ObjectModel]System.ComponentModel.PropertyChangedEventArgs 'FodyTemp.<>PropertyChangedEventArgs'::Foo
	IL_0029: callvirt  instance void FodyTemp.Test::'<>OnPropertyChanged'(class [System.ObjectModel]System.ComponentModel.PropertyChangedEventArgs)

	IL_002E: nop
	IL_002F: ret
} // end of method Test::set_Foo

.method public hidebysig specialname 
	instance void set_Bar (
		valuetype [System.Runtime]System.Nullable`1<valuetype [System.Runtime]System.DateTime> 'value'
	) cil managed 
{
	.custom instance void [System.Runtime]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
		01 00 00 00
	)
	.maxstack 2

	IL_0000: ldarg.0
	IL_0001: call      instance valuetype [System.Runtime]System.Nullable`1<valuetype [System.Runtime]System.DateTime> FodyTemp.Test::get_Bar()
	IL_0006: ldarg.1
	IL_0007: call      bool [System.Runtime]System.Nullable::Equals<valuetype [System.Runtime]System.DateTime>(valuetype [System.Runtime]System.Nullable`1<!!0>, valuetype [System.Runtime]System.Nullable`1<!!0>)
	IL_000C: brfalse.s IL_0010

	IL_000E: br.s      IL_0023

	IL_0010: nop
	IL_0011: ldarg.0
	IL_0012: ldstr     "Bar"
	IL_0017: callvirt  instance void FodyTemp.Test::OnPropertyChanging(string)
	IL_001C: ldarg.0
	IL_001D: ldarg.1
	IL_001E: stfld     valuetype [System.Runtime]System.Nullable`1<valuetype [System.Runtime]System.DateTime> FodyTemp.Test::'<Bar>k__BackingField'

	IL_0023: nop
	IL_0024: ldarg.0
	IL_0025: ldsfld    class [System.ObjectModel]System.ComponentModel.PropertyChangedEventArgs 'FodyTemp.<>PropertyChangedEventArgs'::Bar
	IL_002A: callvirt  instance void FodyTemp.Test::'<>OnPropertyChanged'(class [System.ObjectModel]System.ComponentModel.PropertyChangedEventArgs)
	IL_002F: ret
} // end of method Test::set_Bar