Fix incorrect behavior for empty parameter types, resolves #5

Author: lisachenko

src/ReflectionParameter.php

@@ -264,6 +264,8 @@ public function getType()
             $parameterType = $parameterType->toString();
         } elseif (is_string($parameterType)) {
             $isBuiltin = true;
+        } else {
+            return null;
         }
 
         return new ReflectionType($parameterType, $allowsNull, $isBuiltin);

tests/ReflectionParameterTest.php

@@ -202,6 +202,11 @@ public function testGetTypeMethod()
                         $this->assertSame($originalReturnType->allowsNull(), $parsedReturnType->allowsNull());
                         $this->assertSame($originalReturnType->isBuiltin(), $parsedReturnType->isBuiltin());
                         $this->assertSame($originalReturnType->__toString(), $parsedReturnType->__toString());
+                    } else {
+                        $this->assertSame(
+                            $originalRefParameter->getType(),
+                            $refParameter->getType()
+                        );
                     }
                 }
             }