code: function addModel(model, inputOptions) {
      var options = {
          schemaKey: schemaIds.schema,
          object: model,
          targetObject: state.common.models,
          displayName: 'Model',
          deleteNameFromCommon: true
      };
      applyDefaults(options, inputOptions);
      ensureObjectExists(options);
      cloneObject(options);
      delete options.object.$schema;
      delete options.object.$id;
      var definitions = options.object.definitions;
      delete options.object.definitions;
      applyValidation(options);
      ensureHasName(options);
      ensureNotAlreadyAdded(options);
      setObjectOnTarget(options);
      applyNameDeletion(options);
      if (!definitions) {
          return;
      }
      Object.keys(definitions).forEach(function (key) {
          var definition = _.cloneDeep(definitions[key]);
          definition.name = key;
          addModel(definition, inputOptions);
      });
  }
docs: Adds a common model for later use.
  @param {object} model The schema for the model object to add. Should be a valid [Schema](http://swagger.io/specification/#schemaObject) object.
  @param {AddCommonItemOptions} [inputOptions] - Options to apply when adding the provided item.
  @returns {void}
  @example
  var swagger = require('swagger-spec-express');
  swagger.common.addModel({
  "name": "serverError",
  "type": "object",
  "properties": {
  "message": {
  "type": "string"
  }
  }
  });
  //...
  router.get('/', function (req, res) {
  //...
  }).describe({
  //...
  responses: {
  "500": {
  //...
  model: "serverError"
  }
  }
  //...
  });