NameError:Undefined

[GuGuMur]

Hello!
I'm using Mako to generate wikitext.
I want:

• If song_name2 in the parameters set: return the text;
• If not: no treatment.

My code:

from mako.template import Template
temp = Template("""
% if song_name2:
|second=${song_name2}
% endif
"""))
temp.render(song_name2="Stasis")   #return "|second=Stasis"
temp.render()                      #return NameError:Undefined——I want an empty string.

Thanks!