`ModelBackedDrawable<T>.CreateDrawable()` is R#-annotated to accept
a potentially null model. Apply nullability there too for better reading
experience.
Unfortunately breaks a few classes (which is fixable), and also breaks
Moq/Castle dynamic proxies (which is unfortunate).
Relevant error:
System.TypeLoadException : Method 'GetPanelBackground' in type 'Castle.Proxies.IWorkingBeatmapProxy' from assembly 'DynamicProxyGenAssembly2, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' does not have an implementation.
Stack Trace:
at System.Reflection.Emit.TypeBuilder.CreateTypeNoLock()
at System.Reflection.Emit.TypeBuilder.CreateTypeInfo()
at Castle.DynamicProxy.Generators.Emitters.AbstractTypeEmitter.BuildType()
at Castle.DynamicProxy.Generators.BaseInterfaceProxyGenerator.GenerateType(String typeName, INamingScope namingScope)
at Castle.DynamicProxy.Generators.BaseProxyGenerator.<>c__DisplayClass13_0.<GetProxyType>b__0(CacheKey cacheKey)
at Castle.Core.Internal.SynchronizedDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
at Castle.DynamicProxy.Generators.BaseProxyGenerator.GetProxyType()
at Castle.DynamicProxy.DefaultProxyBuilder.CreateInterfaceProxyTypeWithoutTarget(Type interfaceToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options)
at Castle.DynamicProxy.ProxyGenerator.CreateInterfaceProxyTypeWithoutTarget(Type interfaceToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options)
at Castle.DynamicProxy.ProxyGenerator.CreateInterfaceProxyWithoutTarget(Type interfaceToProxy, Type[] additionalInterfacesToProxy, ProxyGenerationOptions options, IInterceptor[] interceptors)
at Moq.CastleProxyFactory.CreateProxy(Type mockType, IInterceptor interceptor, Type[] interfaces, Object[] arguments) in C:\projects\moq4\src\Moq\Interception\CastleProxyFactory.cs:line 50
In theory it would be possible to fix this via application of
[assembly: InternalsVisibleTo("DynamicProxyGenAssembly2")]
onto the `osu.Game` assembly, but I think this would be bad precedent.
