/**
             * Set nonce header before every Backbone sync.
             *
             * @param {string} method.
             * @param {Backbone.Model} model.
             * @param {{beforeSend}, *} options.
             * @returns {*}.
             */
            sync: function( method, model, options ) {
                var beforeSend;

                options = options || {};

                // Remove date_gmt if null.
                if ( _.isNull( model.get( 'date_gmt' ) ) ) {
                    model.unset( 'date_gmt' );
                }

                // Remove slug if empty.
                if ( _.isEmpty( model.get( 'slug' ) ) ) {
                    model.unset( 'slug' );
                }

                if ( _.isFunction( model.nonce ) && ! _.isUndefined( model.nonce() ) && ! _.isNull( model.nonce() ) ) {
                    beforeSend = options.beforeSend;

                    // @todo enable option for jsonp endpoints
                    // options.dataType = 'jsonp';

                    // Include the nonce with requests.
                    options.beforeSend = function( xhr ) {
                        xhr.setRequestHeader( 'X-WP-Nonce', model.nonce() );

                        if ( beforeSend ) {
                            return beforeSend.apply( this, arguments );
                        }
                    };

                    // Update the nonce when a new nonce is returned with the response.
                    options.complete = function( xhr ) {
                        var returnedNonce = xhr.getResponseHeader( 'X-WP-Nonce' );

                        if ( returnedNonce && _.isFunction( model.nonce ) && model.nonce() !== returnedNonce ) {
                            model.endpointModel.set( 'nonce', returnedNonce );
                        }
                    };
                }

                // Add '?force=true' to use delete method when required.
                if ( this.requireForceForDelete && 'delete' === method ) {
                    model.url = model.url() + '?force=true';
                }
                return Backbone.sync( method, model, options );
            },