Check that activations events are present

Having an empty array, object, or string will now be treated
as no activation events.

This was reported as being confusing since people were just clearing
the array generated by the package generator but their packages weren't
activating.

spec/atom-spec.coffee

@@ -126,6 +126,16 @@ describe "the `atom` global", ->
               expect(eventHandler.callCount).toBe 2
               expect(mainModule.activate.callCount).toBe 1
 
+            it "activates the package immediately when the events are empty", ->
+              mainModule = require './fixtures/packages/package-with-empty-activation-events/index'
+              spyOn(mainModule, 'activate').andCallThrough()
+
+              waitsForPromise ->
+                atom.packages.activatePackage('package-with-empty-activation-events')
+
+              runs ->
+                expect(mainModule.activate.callCount).toBe 1
+
         describe "when the package has no main module", ->
           it "does not throw an exception", ->
             spyOn(console, "error")

spec/fixtures/packages/package-with-empty-activation-events/index.coffee

@@ -0,0 +1 @@
+module.exports = activate: ->

spec/fixtures/packages/package-with-empty-activation-events/package.json

@@ -0,0 +1,5 @@
+{
+  "name": "no events",
+  "version": "0.1.0",
+  "activationEvents": []
+}