Add Layer.image type check

framer/Layer.coffee

@@ -479,6 +479,9 @@ class exports.Layer extends BaseClass
 			@_getPropertyValue "image"
 		set: (value) ->
 
+			if not (_.isString(value) or value is null)
+				layerValueTypeError("image", value)
+
 			currentValue = @_getPropertyValue "image"
 
 			if currentValue == value

test/tests/LayerTest.coffee

@@ -129,15 +129,25 @@ describe "Layer", ->
 			layer.properties.image.should.equal imagePath
 
 		it "should set image", ->
-
 			imagePath = "static/test.png"	
+			layer = new Layer image:imagePath
+			layer.image.should.equal imagePath
 
-			layer = new Layer y:0, \
-				x:0, y:0,
-				width:100, height:100,
-				image:imagePath
+		it "should unset image with null", ->
+			layer = new Layer image:"static/test.png"
+			layer.image = null
+			layer.image.should.equal ""
 
-			layer.image.should.equal imagePath
+		it "should unset image with empty string", ->
+			layer = new Layer image:"static/test.png"
+			layer.image = ""
+			layer.image.should.equal ""
+
+		it "should test image property type", ->
+			f = ->
+				layer = new Layer
+				layer.image = {}
+			f.should.throw()
 
 		it "should set name on create", ->
 			layer = new Layer name:"Test"