Add VRChat and GitHub packages to Unity project

Assets/Udon/Serialization/OdinSerializer/Utilities/Extensions/UnityExtensions.cs

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+//-----------------------------------------------------------------------
+// <copyright file="UnityExtensions.cs" company="Sirenix IVS">
+// Copyright (c) 2018 Sirenix IVS
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+//-----------------------------------------------------------------------
+
+namespace VRC.Udon.Serialization.OdinSerializer.Utilities
+{
+    using System;
+    using System.Reflection;
+
+    /// <summary>
+    /// Extends various Unity classes.
+    /// </summary>
+    public static class UnityExtensions
+    {
+        private static readonly ValueGetter<UnityEngine.Object, IntPtr> UnityObjectCachedPtrFieldGetter;
+
+        static UnityExtensions()
+        {
+            var field = typeof(UnityEngine.Object).GetField("m_CachedPtr", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
+
+            if (field != null)
+            {
+                UnityObjectCachedPtrFieldGetter = EmitUtilities.CreateInstanceFieldGetter<UnityEngine.Object, IntPtr>(field);
+            }
+        }
+
+        /// <summary>
+        /// Determines whether a Unity object is null or "fake null",
+        /// without ever calling Unity's own equality operators.
+        /// This method is useful for checking if a Unity object is
+        /// null, destroyed or missing at times when it is not allowed
+        /// to call Unity's own equality operators, for example when
+        /// not running on the main thread.
+        /// </summary>
+        /// <param name="obj">The Unity object to check.</param>
+        /// <returns>True if the object is null, missing or destroyed; otherwise false.</returns>
+        public static bool SafeIsUnityNull(this UnityEngine.Object obj)
+        {
+            if (object.ReferenceEquals(obj, null))
+            {
+                return true;
+            }
+
+            if (UnityObjectCachedPtrFieldGetter == null)
+            {
+                throw new NotSupportedException("Could not find the field 'm_CachedPtr' in the class UnityEngine.Object; cannot perform a special null check.");
+            }
+
+            IntPtr ptr = UnityObjectCachedPtrFieldGetter(ref obj);
+            return ptr == IntPtr.Zero;
+        }
+    }
+}