This worked for me. In the glideRecord, i have two choices in the dictionary for protocol type. So, I used the corresponding values in the dictionary and it worked.

var populate_modify_network_class = Class.create();
populate_modify_network_class.prototype = Object.extendsObject(AbstractAjaxProcessor, {

    populate_modify_network_function: function() {
        var obj = this.getParameter('sysparm_share');
        var arrayss = {};
        var grec = new GlideRecord('u_cmdb_ci_file_share');
        grec.addQuery('sys_id', obj);
        grec.query();
        if (grec.next()) {
            arrayss.primary = grec.managed_by.toString();
            arrayss.shareType = grec.u_type.getDisplayValue();
			//if condition for protocol
            if (grec.u_protocol.toString() == 'windows_only')
                arrayss.protocol_type = 'windows';
            else
                arrayss.protocol_type = 'multiprotocol';
        }

        return JSON.stringify(arrayss);
    },

    type: 'populate_modify_network_class'
});

Regards

Suman P.