route.get() requires callback functions but got a object undefined at route.(anonymous function)

I checked and tried similar questions like this,but didn't fix the issue.I'm getting route.get() requires callback functions but got a object undefined at route.(anonymous function)

drug.server.policy.js

 'use strict';

    /**
     * Module dependencies
     */
    var acl = require('acl');

    // Using the memory backend
    acl = new acl(new acl.memoryBackend());

    /**
     * Invoke Drugs Permissions
     */
    exports.invokeRolesPolicies = function () {
      acl.allow([{
        roles: ['admin'],
        allows: [{
          resources: '/api/drugs',
          permissions: '*'
        }, {
          resources: '/api/drugs/:drugId',
          permissions: '*'
        }]
      }, {
        roles: ['user'],
        allows: [{
          resources: '/api/drugs',
          permissions: ['get', 'post']
        }, {
          resources: '/api/drugs/:drugId',
          permissions: ['get']
        }]
      }, {
        roles: ['guest'],
        allows: [{
          resources: '/api/drugs',
          permissions: ['get']
        }, {
          resources: '/api/drugs/:drugId',
          permissions: ['get']
        }]
      }]);
    };

    /**
     * Check If Drugs Policy Allows
     */

    exports.isAllowed = function (req, res, next) {
      var roles = (req.user) ? req.user.roles : ['guest'];

      // If an Drug is being processed and the current user created it then allow any manipulation
      if (req.drug && req.user && req.drug.user && req.drug.user.id === req.user.id) {
        return next();
      }

      // Check for user roles
      acl.areAnyRolesAllowed(roles, req.route.path, req.method.toLowerCase(), function (err, isAllowed) {
        if (err) {
          // An authorization error occurred
          return res.status(500).send('Unexpected authorization error');
        } else {
          if (isAllowed) {
            // Access granted! Invoke next middleware
            return next();
          } else {
            return res.status(403).json({
              message: 'User is not authorized'
            });
          }
        }
      });
    };

drug.server.routes.js

'use strict';

/**
 * Module dependencies
 */
var drugsPolicy = require('../policies/drugs.server.policy'),
  drugs = require('../controllers/drugs.server.controller');

module.exports = function(app) {
  // Prescriptions Routes

  app.route('/api/drugs').all(drugsPolicy.isAllowed)
    .get(drugs.list)
    .post(drugs.create);

  app.route('/api/drugs/:drugId').all(drugsPolicy.isAllowed)
    .get(drugs.read)
    .put(drugs.update)
    .delete(drugs.delete);

  // Finish by binding the DrugPrescription middleware
  app.param('drugId', drugs.drugByID);
};

drugs.server.controller.js

 'use strict';

    /**
     * Module dependencies.
     */
    var path = require('path'),
      mongoose = require('mongoose'),
      Drug
 = mongoose.model('Drug'),
      errorHandler = require(path.resolve('./modules/core/server/controllers/errors.server.controller')),
      _ = require('lodash');

    /**
     * Create a Drug
     */
    exports.create = function(req, res) {
      var drug = new Drug(req.body);
      drug.user = req.user;

      drug.save(function(err) {
        if (err) {
          return res.status(400).send({
            message: errorHandler.getErrorMessage(err)
          });
        } else {
          res.jsonp(drug);
        }
      });
    };

    /**
     * Show the current Drug
     */
    exports.read = function(req, res) {
        // convert mongoose document to JSON
      var drug = req.drug ? req.drug.toJSON() : {};

        // Add a custom field to the Article, for determining if the current User is the "owner".
        // NOTE: This field is NOT persisted to the database, since it doesn't exist in the Article model.
      drug.isCurrentUserOwner = req.user && drug.user && drug.user._id.toString() === req.user._id.toString();

      res.jsonp(drug);
    };

    /**
     * Update a Drug
     */
    exports.update = function(req, res) {
      var drug = req.drug;

      drug = _.extend(drug, req.body);

      drug.save(function(err) {
        if (err) {
          return res.status(400).send({
            message: errorHandler.getErrorMessage(err)
          });
        } else {
          res.jsonp(drug);
        }
      });
    };

    /**
     * Delete an Drug
     */
    exports.delete = function(req, res) {
      var drug = req.drug;

      drug.remove(function(err) {
        if (err) {
          return res.status(400).send({
            message: errorHandler.getErrorMessage(err)
          });
        } else {
          res.jsonp(drug);
        }
      });
    };

    /**
     * List of Drug
     */
    exports.list = function(req, res) {
      Drug.find().sort('-created').populate('user', 'displayName').exec(function(err, drugs) {
        if (err) {
          return res.status(400).send({
            message: errorHandler.getErrorMessage(err)
          });
        } else {
          res.jsonp(drugs);
        }
      });
    };

    /**
     * Drug middleware
     */
    exports.drugByID = function(req, res, next, id) {

      if (!mongoose.Types.ObjectId.isValid(id)) {
        return res.status(400).send({
          message: 'Drug is invalid'
        });
      }

      Drug.findById(id).populate('user', 'displayName').exec(function (err, drug) {
        if (err) {
          return next(err);
        } else if (!drug) {
          return res.status(404).send({
            message: 'No Drug with that identifier has been found'
          });
        }
        req.drug = drug;
        next();
      });
    };

Stack Link:http://stackoverflow.com/questions/43830988/route-get-requires-callback-functions-but-got-a-object-undefined-at-route-ano