diff --git a/.travis.yml b/.travis.yml
index d5a6f64..e1af48a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,6 +2,9 @@ language: python
 
 matrix:
   include:
+    - python: 3.5
+    - python: 3.6
+    - python: 3.7
     - python: 3.8
     - python: 3.9
       dist: xenial
diff --git a/mypy.ini b/mypy.ini
index 1b62896..8a9821a 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -5,3 +5,6 @@ scripts_are_modules = True
 warn_unused_configs = True
 disallow_untyped_calls = True
 check_untyped_defs = True
+
+[mypy-pytz.*]
+ignore_missing_imports = True
diff --git a/pydfs_lineup_optimizer/player_pool.py b/pydfs_lineup_optimizer/player_pool.py
index b066104..a9925c0 100644
--- a/pydfs_lineup_optimizer/player_pool.py
+++ b/pydfs_lineup_optimizer/player_pool.py
@@ -1,4 +1,4 @@
-from typing import FrozenSet, List, Optional, Set, Union, Iterable, Dict, Literal, DefaultDict
+from typing import FrozenSet, List, Optional, Set, Union, Iterable, Dict, DefaultDict
 from collections import defaultdict
 from itertools import chain
 from pydfs_lineup_optimizer.settings import BaseSettings
@@ -23,8 +23,9 @@ def __init__(
             to_value: Optional[float] = None,
             positions: Optional[Iterable[str]] = None,
             teams: Optional[Iterable[str]] = None,
-            filter_by: Literal['fppg', 'efficiency', 'salary'] = 'fppg',
+            filter_by: str = 'fppg',
     ):
+        assert filter_by in ('fppg', 'efficiency', 'salary')
         self.from_value = from_value
         self.to_value = to_value
         self.positions = frozenset(positions or [])
@@ -247,7 +248,6 @@ def unlock_player(self, player: DirtyPlayer):
         del self._locked_players[player]
 
     def get_players(self, *players_and_groups: Union[DirtyPlayer, PlayerFilter]) -> List[Player]:
-        result = []
         players, filters = [], []
         for item in players_and_groups:
             if isinstance(item, BaseFilter):
@@ -261,11 +261,13 @@ def get_players(self, *players_and_groups: Union[DirtyPlayer, PlayerFilter]) ->
                 all(player_filter.filter(player, False) for player_filter in filters)
             }
         if players:
+            result = []
             for player in players:
                 cleaned_player = self._clean_player(player, allowed_players=allowed_players)
                 if cleaned_player:
                     result.append(cleaned_player)
-        return result
+            return result
+        return list(allowed_players) if allowed_players else self.all_players
 
     def add_filters(self, *filters: BaseFilter):
         self._player_filters.extend(filters)
diff --git a/tox.ini b/tox.ini
index 3603f99..ba9aaa6 100644
--- a/tox.ini
+++ b/tox.ini
@@ -3,6 +3,9 @@ envlist = mypy,py35-{pulp,mip},py36-{pulp,mip},py37-{pulp,mip},py38-{pulp,mip},p
 
 [travis]
 python =
+    3.5: py35,
+    3.6: py36,
+    3.7: py37,
     3.8: py38,
     3.9: py39, mypy