Fix showing 0.0.0 version

pipdeps/pipdeps.py

@@ -55,6 +55,8 @@ def upgrade_package(data):
     """
     pip install --upgrade "<package>==<versions>"
     """
+    if not data:
+        return
     to_upgrade = []
     for package, version in data:
         to_upgrade.append("%s==%s" % (package, version))