Index: pluginconf/depends.py
==================================================================
--- pluginconf/depends.py
+++ pluginconf/depends.py
@@ -38,16 +38,16 @@
         find_executable = lambda name: False
 
 
 # Minimal depends: probing
 # ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
-class Check(object):
+class Check():
     """
     Now this definitely requires customization. Each plugin can carry
     a list of (soft-) dependency names.
 
-    \# depends: config, appcore >= 2.0, bin:wkhtmltoimage, python < 3.5
+    … # depends: config, appcore >= 2.0, bin:wkhtmltoimage, python < 3.5
 
     Here only in-application modules are honored, system references
     ignored. Unknown plugin names are also skipped. A real install
     helper might want to auto-tick them on, etc. This example is just
     meant for probing downloadable plugins.
@@ -76,11 +76,11 @@
     log = logging.getLogger("pluginconf.dependency")
 
     # ignore bin:… or python:… package in depends
     system_deps = False
 
-    def __init__(self, add={}, core=["st2", "uikit", "config", "action"]):
+    def __init__(self, add=None, core=["st2", "uikit", "config", "action"]):
         """
         Prepare list of known plugins and versions in self.have={}
 
         Parameters
         ----------
@@ -93,11 +93,11 @@
         self.have = {
             "python": {"version": sys.version}
         }
 
         # inject virtual modules
-        for name, meta in add.items():
+        for name, meta in (add or {}).items():
             if isinstance(meta, bool):
                 meta = 1 if meta else -1
             if isinstance(meta, tuple):
                 meta = ".".join(str(n) for n in meta)
             if isinstance(meta, (int, float, str)):