title: How to assign default value if env var is empty?
body: <p>How do you assign a default value if an environment variable isn't set in Go?</p>
  
  <p>In Python I could do <code>mongo_password = os.getenv('MONGO_PASS', 'pass')</code> where <code>pass</code> is the default value if <code>MONGO_PASS</code> env var isn't set.</p>
  
  <p>I tried an if statement based on <code>os.Getenv</code> being empty, but that doesn't seem to work due to the scope of variable assignment within an if statement. And I'm checking for multiple env var's, so I can't act on this information within the if statement.</p>