diff --git a/filter2.py b/filter2.py
index 4af8680..7f30d68 100644
--- a/filter2.py
+++ b/filter2.py
@@ -60,8 +60,9 @@ def toldapfilter(l):
 txt = "".join(c for c in pyparsing.printables if c not in '()&|!=')
 expr = pyparsing.nestedExpr("(", ")", pyparsing.Word(txt) | pyparsing.oneOf("& | != ="))
 	
-def human_to_ldap(data):
-	data='(%s)' % data
-	l=expr.parseString(data).asList()
-	return "(%s)" % toldapfilter(collapse(toprefix(prioritize(l))))
+def human_to_list(data):
+    if data:
+        return collapse(toprefix(prioritize(expr.parseString("(%s)" % data).asList())))
 
+def human_to_ldap(data):
+	return "(%s)" % toldapfilter(human_to_list(data))
diff --git a/filter3.py b/filter3.py
index 2989deb..7b75218 100644
--- a/filter3.py
+++ b/filter3.py
@@ -43,6 +43,10 @@ def toldapfilter(l):
 		return "!(%s=%s)" % (l[1], l[2])
 	return op + ''.join(['(%s)' % toldapfilter(i) for i in l[1:]])
 	
-def human_to_ldap(str):
-	return "(%s)" % toldapfilter(toprefix(simplify(expr.parseString(str).asList())))
+def human_to_list(data):
+    if data:
+        return toprefix(simplify(expr.parseString(data).asList()))
+
+def human_to_ldap(data):
+        return "(%s)" % toldapfilter(human_to_list(data))