Drawloop Button: Specific error for multiple criteria

Problem:

Members of the Sales Team must fill in the Next Step and Campaign fields on an Opportunity in order to generate a Quote document using Nintex Drawloop Document Generation. If the ‘Generate Documents’ button is clicked and one of the fields is blank an error message specifying the blank field should be presented to the user.

Solution:

Use the sample syntax below:

{!REQUIRESCRIPT("/soap/ajax/26.0/connection.js")}
if ('{!Opportunity.NextStep}' == '' )
alert('You cannot generate a quote unless Next Step has a value.');
else if ('{!Opportunity.Campaign}' == '' )
alert('You cannot generate a quote unless Campaign has a value.');
else
window.location.href = '/apex/loop__looplus?eid={!Opportunity.Id}&accountId={!Opportunity.AccountId}&sessionId={!$Api.Session_ID}';