diff --git a/scripttest.py b/scripttest.py
index d00247e..1c5d0d9 100644
--- a/scripttest.py
+++ b/scripttest.py
@@ -24,6 +24,9 @@ def clean_environ(e):
 
 
 def string(string):
+    if string is None:
+        # This function should always return a string and "None" is truthy.
+        return ''
     if sys.version_info >= (3,):
         if isinstance(string, str):
             return string
@@ -207,6 +210,8 @@ def run(self, script, *args, **kw):
         ``quiet``: (default False)
             When there's an error (return code != 0), do not print
             stdout/stderr
+        ``debug``: (default False)
+            Print lots of information about the running subprocess
 
         Returns a `ProcResult
         <class-paste.fixture.ProcResult.html>`_ object.