Storage - Use nullable reference types

Core - Fix build warnings

src/Artemis.Core/Plugins/LayerBrushes/LayerBrushDescriptor.cs

@@ -65,7 +65,7 @@ public class LayerBrushDescriptor
         BaseLayerBrush brush = (BaseLayerBrush) Provider.Plugin.Resolve(LayerBrushType);
         brush.Layer = layer;
         brush.Descriptor = this;
-        brush.LayerBrushEntity = entity ?? new LayerBrushEntity {ProviderId = Provider.Id, BrushType = LayerBrushType.FullName};
+        brush.LayerBrushEntity = entity ?? new LayerBrushEntity {ProviderId = Provider.Id, BrushType = LayerBrushType.FullName ?? throw new InvalidOperationException()};
 
         brush.Initialize();
         return brush;

src/Artemis.Core/Plugins/LayerEffects/Internal/BaseLayerEffect.cs

@@ -231,7 +231,7 @@ public abstract class BaseLayerEffect : BreakableModel, IDisposable, IStorageMod
             return;
 
         LayerEffectEntity.ProviderId = Descriptor.Provider.Id;
-        LayerEffectEntity.EffectType = GetType().FullName;
+        LayerEffectEntity.EffectType = GetType().FullName ?? throw new InvalidOperationException();
         BaseProperties?.ApplyToEntity();
         LayerEffectEntity.PropertyGroup = BaseProperties?.PropertyGroupEntity;
     }

src/Artemis.Core/Plugins/Settings/PluginSettings.cs

@@ -41,7 +41,7 @@ public class PluginSettings
             if (_settingEntities.ContainsKey(name))
                 return (PluginSetting<T>) _settingEntities[name];
             // Try to find in database
-            PluginSettingEntity settingEntity = _pluginRepository.GetSettingByNameAndGuid(name, Plugin.Guid);
+            PluginSettingEntity? settingEntity = _pluginRepository.GetSettingByNameAndGuid(name, Plugin.Guid);
             // If not found, create a new one
             if (settingEntity == null)
             {