title: Json schema not validating required attribute
body: <p>i'm coding the following Json Schema:</p>
  
  <pre><code>{
    "$schema": "http://json-schema.org/schema#",
    "title": "Layout",
    "description": "The layout created by the user",
    "type": "object",
    "definitions": {
      "stdAttribute": {
        "type": "object",
        "properties": {
          "attributeValue": {
            "type": "object"
          },
          "attributeName": {
            "type": "string"
          }
        }
      },
      "stdItem": {
        "type": "object",
        "required" : ["stdAttributes"],
        "properties": {
          "stdType": {
            "enum": [
              "CONTAINER",
              "TEXT",
              "TEXTAREA",
              "BUTTON",
              "LABEL",
              "IMAGE",
              "MARCIMAGE",
              "DATA",
              "SELECT",
              "TABLE"
            ]
          },
          "stdAttributes": {
            "type": "array",
            "items": {
              "$ref": "#/definitions/stdAttribute"
            },
            "minItems": 1
          },
          "children": {
            "type": "array",
            "items": {
              "$ref": "#/definitions/stdItem"
            }
          }
        }
      }
    }
  }
  </code></pre>
  
  <p>When i set the following data:</p>
  
  <pre><code>{
      "stdItem": {
        "stdType": "CONTAINER",
        "stdAttributes": [],
        "children": []
    }
  }
  </code></pre>
  
  <p>the validator says there is no error but in the schema i'm using a minItems and a ref to the <strong>"StdAttribute"</strong> schema in <strong>"StdAttributtes"</strong>.</p>
  
  <p>I tried to define this property in the base schema but the validator says the same thing.</p>
  
  <p>How should i validate the type and number of items in "StdAttributes"?</p>
  
  <p>I'm using the Java Validator.</p>