1.8.0: Added AssetsOnly, SceneObjectsOnly, AssignAssetIfNull, AssignComponentIfNull

- Attributes: Added AssetsOnly, SceneObjectsOnly, AssignAssetIfNull, AssignComponentIfNull
- Attributes: Replaced AssignIfNull with AssignComponentIfNull

Editor/ValueModifiers/AssetsOnlyAttributeDrawer.cs

@@ -0,0 +1,25 @@
+using UnityEditor;
+using UnityEngine;
+
+namespace Module.Inspector.Editor
+{
+    [CustomPropertyDrawer(typeof(AssetsOnlyAttribute))]
+    internal sealed class AssetsOnlyAttributeDrawer : ValueModifierPropertyDrawer
+    {
+        public override void Modify(ValueModifierPropertyAttribute attribute, SerializedProperty property)
+        {
+            if (property.propertyType != SerializedPropertyType.ObjectReference)
+                return;
+            
+            Object obj = property.objectReferenceValue;
+
+            if (obj != null && !IsValid(obj))
+                property.objectReferenceValue = null;
+        }
+
+        private static bool IsValid(Object obj)
+        {
+            return AssetDatabase.Contains(obj);
+        }
+    }
+}