Fix SkipRepeatsQueue._put() raises AttributeError (#817)

This fixes an issue with SkipRepeatsQueue._put() which causes it to raise
an AttributeError on the first put. This is done by adding a check to test
if _last_item is set to None, which is the value set by __init__()

src/watchdog/utils/bricks.py

@@ -87,7 +87,7 @@ def _init(self, maxsize):
         self._last_item = None
 
     def _put(self, item):
-        if item != self._last_item:
+        if self._last_item is None or item != self._last_item:
             super()._put(item)
             self._last_item = item
         else:

tests/test_skip_repeats_queue.py

@@ -16,6 +16,7 @@
 # limitations under the License.
 
 import pytest
+import watchdog.events as events
 from watchdog.utils.bricks import SkipRepeatsQueue
 
 from .markers import cpython_only
@@ -58,6 +59,18 @@ def test_allow_nonconsecutive():
     assert q.empty()
 
 
+def test_put_with_watchdog_events():
+    # FileSystemEvent.__ne__() uses the key property without
+    # doing any type checking. Since _last_item is set to
+    # None in __init__(), an AttributeError is raised when
+    # FileSystemEvent.__ne__() tries to use None.key
+    queue = SkipRepeatsQueue()
+    dummy_file = 'dummy.txt'
+    event = events.FileCreatedEvent(dummy_file)
+    queue.put(event)
+    assert queue.get() is event
+
+
 def test_prevent_consecutive():
     q = SkipRepeatsQueue()