Fix setting empty entities in Example.from_dict (#8426)

spacy/tests/training/test_new_example.py

@@ -182,6 +182,27 @@ def test_Example_from_dict_with_entities(annots):
     assert example.reference[5].ent_type_ == "LOC"
 
 
+def test_Example_from_dict_with_empty_entities():
+    annots = {
+        "words": ["I", "like", "New", "York", "and", "Berlin", "."],
+        "entities": [],
+    }
+    vocab = Vocab()
+    predicted = Doc(vocab, words=annots["words"])
+    example = Example.from_dict(predicted, annots)
+    # entities as empty list sets everything to O
+    assert example.reference.has_annotation("ENT_IOB")
+    assert len(list(example.reference.ents)) == 0
+    assert all(token.ent_iob_ == "O" for token in example.reference)
+    # various unset/missing entities leaves entities unset
+    annots["entities"] = None
+    example = Example.from_dict(predicted, annots)
+    assert not example.reference.has_annotation("ENT_IOB")
+    annots.pop("entities", None)
+    example = Example.from_dict(predicted, annots)
+    assert not example.reference.has_annotation("ENT_IOB")
+
+
 @pytest.mark.parametrize(
     "annots",
     [

spacy/training/example.pyx

@@ -420,7 +420,7 @@ def _fix_legacy_dict_data(example_dict):
     token_dict = example_dict.get("token_annotation", {})
     doc_dict = example_dict.get("doc_annotation", {})
     for key, value in example_dict.items():
-        if value:
+        if value is not None:
             if key in ("token_annotation", "doc_annotation"):
                 pass
             elif key == "ids":