Add test for #1757: Comparison against None

spacy/lexeme.pyx

@@ -40,6 +40,11 @@ cdef class Lexeme:
         assert self.c.orth == orth
 
     def __richcmp__(self, other, int op):
+        if other is None:
+            if op == 0 or op == 1 or op == 2:
+                return False
+            else:
+                return True
         if isinstance(other, Lexeme):
             a = self.orth
             b = other.orth

spacy/tests/regression/test_issue1757.py

@@ -0,0 +1,18 @@
+'''Test comparison against None doesn't cause segfault'''
+from __future__ import unicode_literals
+
+from ...tokens import Doc
+from ...vocab import Vocab
+
+def test_issue1757():
+    doc = Doc(Vocab(), words=['a', 'b', 'c'])
+    assert not doc[0] < None
+    assert not doc[0] == None
+    assert doc[0] >= None
+    span = doc[:2]
+    assert not span < None
+    assert not span == None
+    assert span >= None
+    lex = vocab['a']
+    assert not lex == None
+    assert not lex < None