[Migrated] Fix when no expressions or keep_warm is false

[jneves]

Originally from: Miserlou/Zappa#2185 by manycoding

When I set keep_warm_expression it fails with

    events=events
  File "/Users/valery/.local/share/virtualenvs/document_data_extract_zappa-j8vc3Vbe/lib/python3.6/site-packages/zappa/core.py", line 2783, in schedule_events
    print("Could not create event {} - Please define either an expression or an event source".format(name))
UnboundLocalError: local variable 'name' referenced before assignment

So I fixed it.

Description

GitHub Issues