fix for

Traceback (most recent call last):
  File "./manage.py", line 59, in <module>
    execute_from_command_line(sys.argv)
  File "/home/ubuntu/gitcoin/gitcoin-37/lib/python3.7/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "/home/ubuntu/gitcoin/gitcoin-37/lib/python3.7/site-packages/django/core/management/__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/ubuntu/gitcoin/gitcoin-37/lib/python3.7/site-packages/django/core/management/base.py", line 323, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/ubuntu/gitcoin/gitcoin-37/lib/python3.7/site-packages/django/core/management/base.py", line 364, in execute
    output = self.handle(*args, **options)
  File "/home/ubuntu/gitcoin/coin/app/marketing/management/commands/assemble_leaderboards.py", line 517, in handle
    do_leaderboard()
  File "/home/ubuntu/gitcoin/coin/app/marketing/management/commands/assemble_leaderboards.py", line 453, in do_leaderboard
    index_terms = bounty_index_terms(b)
  File "/home/ubuntu/gitcoin/coin/app/marketing/management/commands/assemble_leaderboards.py", line 170, in bounty_index_terms
    for keyword in bounty_to_city(bounty):
  File "/home/ubuntu/gitcoin/coin/app/marketing/management/commands/assemble_leaderboards.py", line 157, in bounty_to_city
    return list(set(ele['city'] for ele in bounty_to_location(bounty) if ele and ele.get('city')))
  File "/home/ubuntu/gitcoin/coin/app/marketing/management/commands/assemble_leaderboards.py", line 112, in bounty_to_location
    locations = locations + profile_to_location(username)
  File "/home/ubuntu/gitcoin/coin/app/marketing/management/commands/assemble_leaderboards.py", line 91, in profile_to_location
    results = profile_to_location_helper(handle)
  File "/home/ubuntu/gitcoin/coin/app/marketing/management/commands/assemble_leaderboards.py", line 99, in profile_to_location_helper
    profiles = Profile.objects.filter(handle=handle.lower())
AttributeError: 'NoneType' object has no attribute 'lower'

app/marketing/management/commands/assemble_leaderboards.py

@@ -95,7 +95,9 @@ def profile_to_location(handle):
 
 
 def profile_to_location_helper(handle):
-
+    if not handle:
+        return []
+
     profiles = Profile.objects.filter(handle=handle.lower())
     if handle and profiles.exists():
         profile = profiles.first()