Ignore empty lock files

waflib/Scripting.py

@@ -91,6 +91,8 @@ def waf_entry_point(current_directory, version, wafdir):
 			else:
 				# check if the folder was not moved
 				for x in (env.run_dir, env.top_dir, env.out_dir):
+					if not x:
+						continue
 					if Utils.is_win32:
 						if cur == x:
 							load = True