Treat nullable warnings as errors

src/ChunkyImageLib/ChunkyImageLib.csproj

@@ -4,6 +4,7 @@
     <TargetFramework>net6.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
+    <WarningsAsErrors>Nullable</WarningsAsErrors>
     <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
   </PropertyGroup>
 

src/PixiEditor.ChangeableDocument/PixiEditor.ChangeableDocument.csproj

@@ -4,6 +4,7 @@
     <TargetFramework>net6.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
+    <WarningsAsErrors>Nullable</WarningsAsErrors>
   </PropertyGroup>
 
   <ItemGroup>

src/PixiEditor.Zoombox/PixiEditor.Zoombox.csproj

@@ -4,6 +4,7 @@
     <TargetFramework>net6.0-windows</TargetFramework>
     <Nullable>enable</Nullable>
     <UseWPF>true</UseWPF>
+    <WarningsAsErrors>Nullable</WarningsAsErrors>
   </PropertyGroup>
 
   <ItemGroup>

src/PixiEditorPrototype/PixiEditorPrototype.csproj

@@ -5,6 +5,7 @@
     <TargetFramework>net6.0-windows</TargetFramework>
     <Nullable>enable</Nullable>
     <UseWPF>true</UseWPF>
+    <WarningsAsErrors>Nullable</WarningsAsErrors>
   </PropertyGroup>
 
   <ItemGroup>