Fixed a problem with observers accepting zero arguments.

Author: james-turner

src/Observable/Notifier.php

@@ -130,8 +130,9 @@ private function dequeueEvent(){
      */
     private function determineType(callable $callable){
         $reflector = $this->reflect($callable);
-        if ($reflector->getNumberOfParameters() != 1) throw new \InvalidArgumentException("Observers must ONLY accept 1 parameter.");
-        $type = $reflector->getParameters()[0]->getClass();
+        if ($reflector->getNumberOfParameters() > 1) throw new \InvalidArgumentException("Observers must ONLY accept 1 parameter.");
+        $reflectionParameters = $reflector->getParameters();
+        $type = count($reflectionParameters)?$reflectionParameters[0]->getClass():null;
         return $type?$type->getName():null;
     }
 

test/Observable/Test/ObservableTest.php

@@ -114,6 +114,16 @@ public function testObserverRemoval(){
 
     }
 
+    public function testAllowsZeroArgumentsObservers(){
+        $func = function()use(&$happened){
+            $happened = true;
+        };
+        $this->addObserver($func);
+
+        $this->notifyObservers(1);
+        $this->assertThat($happened, $this->isTrue());
+    }
+
 
     public function verifyEvent($event){
         $this->assertThat(count($this->events), $this->equalTo(1));