http://anchan828.hatenablog.jp/entry/2013/05/12/021914のエラー修正版

DrawComponentIconInHierarchy.cs

using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

[InitializeOnLoad]
/// <summary>
/// Draw component icon in hierarchy.
/// </summary>
public class DrawComponentIconInHierarchy
{
	const int iconSize = 16;

	/// <summary>
	/// Initializes the <see cref="DrawComponentIconInHierarchy"/> class.
	/// </summary>
	static DrawComponentIconInHierarchy()
	{
		EditorApplication.hierarchyWindowItemOnGUI += (instanceID, rect) =>
		{
			DrawComponentIcons(instanceID, rect);
		};
	}

	/// <summary>
	/// Draws the component icons.
	/// </summary>
	/// <param name="instanceID">Instance I.</param>
	/// <param name="rect">Rect.</param>
	static void DrawComponentIcons(int instanceID, Rect rect)
	{
		rect.x += rect.width;
		rect.width = iconSize;

		HashSet<Component> components = GetComponents(instanceID);
		if(components == null)
		{
			return;
		}

		HashSet<Texture> textures = new HashSet<Texture>();

		foreach(Component component in components)
		{
			if(component != null)
			{
				textures.Add(AssetPreview.GetMiniThumbnail(component));
			}
		}

		foreach(var texture in textures)
		{
			rect.x -= iconSize;
			GUI.DrawTexture(rect, texture);
		}
	}

	/// <summary>
	/// Gets the components.
	/// </summary>
	/// <returns>The components.</returns>
	/// <param name="instanceID">Instance I.</param>
	static HashSet<Component> GetComponents(int instanceID)
	{
		HashSet <Component> components = new HashSet<Component>();
		GameObject sceneGameObject = EditorUtility.InstanceIDToObject(instanceID) as GameObject;
		if(sceneGameObject == null)
		{
			return null;
		}

		var sceneGameObjectComponents = sceneGameObject.GetComponents<Component>();
		if(sceneGameObjectComponents == null)
		{
			return null;
		}

		foreach(Component component in sceneGameObjectComponents)
		{
			if(component is UnityEngine.Transform)
			{
				continue;
			}
			components.Add(component);
		}
		return components;
	}
}