Fix a case when HOME is set but empty

cdist/__init__.py

@@ -175,6 +175,11 @@ def str_hash(s):
 
 def home_dir():
     if 'HOME' in os.environ:
-        return os.path.join(os.environ['HOME'], ".cdist")
+        home = os.environ['HOME']
+        if home:
+            rv = os.path.join(home, ".cdist")
         else:
-        return None
+            rv = None
+    else:
+        rv = None
+    return rv

docs/changelog

@@ -6,6 +6,7 @@ next:
 	* Core: Add -4 and -6 params to force IPv4, IPv6 addresses respectively (Darko Poljak)
 	* Type __package_update_index: Fix messaging (Thomas Eckert)
 	* Type __package_dpkg: Add state parameter and messaging (Thomas Eckert)
+	* Core: Fix a case when HOME is set but empty (Darko Poljak)
 
 4.8.0: 2018-02-14
 	* Core: Skip empty lines in parameter files (Darko Poljak)