softwaretype recipe: all falsy parameter values are ignored.

slapos/recipe/softwaretype.py

@@ -114,6 +114,10 @@ class Recipe:
     if not buildout.has_section('slap-parameter'):
       buildout.add_section('slap-parameter')
     for parameter, value in self.parameter_dict.items():
+      # All parameters evaluating to False are... False, and shouldn't
+      # convey any information.
+      # Here, all those parameters are set to empty string.
+      if value:
         if isinstance(value, str):
           buildout.set('slap-parameter', parameter, value)
         else: