Allow canceling render

lib/Component.lua

@@ -131,6 +131,11 @@ function Component:setState(partialState)
 	-- If the partial state is a function, invoke it to get the actual partial state.
 	if type(partialState) == "function" then
 		partialState = partialState(self.state, self.props)
+
+		-- If partialState is nil, abort the render.
+		if partialState == nil then
+			return
+		end
 	end
 
 	local newState = {}

lib/Component.spec.lua

@@ -374,5 +374,38 @@ return function()
 
 			Reconciler.teardown(instance)
 		end)
+
+		it("should cancel rendering if the function returns nil", function()
+			local TestComponent = Component:extend("TestComponent")
+			local setStateCallback
+			local renderCount = 0
+
+			function TestComponent:init()
+				setStateCallback = function(newState)
+					self:setState(newState)
+				end
+
+				self.state = {
+					value = 0
+				}
+			end
+
+			function TestComponent:render()
+				renderCount = renderCount + 1
+				return nil
+			end
+
+			local element = Core.createElement(TestComponent)
+			local instance = Reconciler.reify(element)
+			expect(renderCount).to.equal(1)
+
+			setStateCallback(function(state, props)
+				return nil
+			end)
+
+			expect(renderCount).to.equal(1)
+
+			Reconciler.teardown(instance)
+		end)
 	end)
 end