Two misc changes: Fix error message and fix copyright (with check)

.github/workflows/check_license.yml

@@ -0,0 +1,28 @@
+---
+name: Check license
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  test_license:
+    name: Check license headers
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Get changed files
+       id: changed-files
+       uses: tj-actions/[email protected]
+
+    - name: Check copyright header in added files
+    - shell: bash
+    - run: |
+        missing=0
+        for file in "${{ steps.changed-files.outputs.added_files }}"; do
+          if ! egrep -q '(Facebook, Inc(\.|,)? and its affiliates)|([0-9]{4}-present(\.|,)? Facebook)|([0-9]{4}(\.|,)? Facebook)' $file
+          echo "Missing copyright header in $file"
+          missing=$(expr $missing + 1)
+        done
+        exit $missing

.github/workflows/test_and_deploy.yml

@@ -142,4 +142,3 @@ jobs:
       with:
         user: __token__
         password: ${{ secrets.PYPI_TOKEN }}
-...

nle/env/base.py

@@ -255,7 +255,7 @@ def __init__(
             actions = FULL_ACTIONS
         self._actions = actions
 
-        self.last_observation = None
+        self.last_observation = ()
 
         try:
             if savedir is None:

nle/tests/test_envs.py

@@ -385,6 +385,22 @@ def test_final_reward(self, env):
         assert reward == 0.0
 
 
+class TestEnvMisc:
+    """Tests miscellaneous enviroment behavior."""
+
+    @pytest.fixture
+    def env(self):
+        e = gym.make("NetHackScore-v0")
+        try:
+            yield e
+        finally:
+            e.close()
+
+    def test_no_reset(self, env):
+        with pytest.raises(RuntimeError, match="step called without reset()"):
+            env.step(0)
+
+
 class TestNetHackChallenge:
     def test_no_seed_setting(self):
         env = gym.make("NetHackChallenge-v0")

nle/tests/test_system.py

@@ -1,3 +1,4 @@
+# Copyright (c) Facebook, Inc. and its affiliates.
 import multiprocessing as mp
 
 import gym