Ensure semantics of empty array and null are correctly presented

Fixes #33

Author: cebe

src/spec/Operation.php

@@ -51,6 +51,13 @@ protected function attributes(): array
         ];
     }
 
+    protected function attributeDefaults(): array
+    {
+        return [
+            'security' => null,
+        ];
+    }
+
     /**
      * Perform validation on this object, check data against OpenAPI Specification rules.
      *

tests/spec/SecuritySchemeTest.php

@@ -170,4 +170,39 @@ public function testSecurityRequirement()
 
         $this->assertSame(['write:pets', 'read:pets'], $securityRequirement->petstore_auth);
     }
+
+    public function testDefaultSecurity()
+    {
+        $openapi = Reader::readFromYaml(<<<YAML
+paths:
+  /path/one:
+    post:
+      description: path one
+      # [...]
+      security: [] # default security
+
+  /path/two:
+    post:
+      description: path two
+      # [...]
+      # No security entry defined there
+
+components:
+  securitySchemes:
+    Bearer:
+      type: http
+      scheme: bearer
+      bearerFormat: JWT
+
+security:
+  - Bearer: []
+YAML
+        );
+
+        $this->assertSame([], $openapi->paths->getPath('/path/one')->post->security);
+        $this->assertSame(null, $openapi->paths->getPath('/path/two')->post->security);
+
+        $this->assertCount(1, $openapi->security);
+        $this->assertSame([], $openapi->security[0]->Bearer);
+    }
 }