Check for any non-Doc returned value for components (#11424)

spacy/errors.py

@@ -230,8 +230,9 @@ class Errors(metaclass=ErrorsWithCodes):
             "initialized component.")
     E004 = ("Can't set up pipeline component: a factory for '{name}' already "
             "exists. Existing factory: {func}. New factory: {new_func}")
-    E005 = ("Pipeline component '{name}' returned None. If you're using a "
-            "custom component, maybe you forgot to return the processed Doc?")
+    E005 = ("Pipeline component '{name}' returned {returned_type} instead of a "
+            "Doc. If you're using a custom component, maybe you forgot to "
+            "return the processed Doc?")
     E006 = ("Invalid constraints for adding pipeline component. You can only "
             "set one of the following: before (component name or index), "
             "after (component name or index), first (True) or last (True). "

spacy/language.py

@@ -1028,8 +1028,8 @@ class Language:
                 raise ValueError(Errors.E109.format(name=name)) from e
             except Exception as e:
                 error_handler(name, proc, [doc], e)
-            if doc is None:
-                raise ValueError(Errors.E005.format(name=name))
+            if not isinstance(doc, Doc):
+                raise ValueError(Errors.E005.format(name=name, returned_type=type(doc)))
         return doc
 
     def disable_pipes(self, *names) -> "DisabledPipes":

spacy/tests/test_language.py

@@ -670,3 +670,25 @@ def test_dot_in_factory_names(nlp):
 
     with pytest.raises(ValueError, match="not permitted"):
         Language.factory("my.evil.component.v1", func=evil_component)
+
+
+def test_component_return():
+    """Test that an error is raised if components return a type other than a
+    doc."""
+    nlp = English()
+
+    @Language.component("test_component_good_pipe")
+    def good_pipe(doc):
+        return doc
+
+    nlp.add_pipe("test_component_good_pipe")
+    nlp("text")
+    nlp.remove_pipe("test_component_good_pipe")
+
+    @Language.component("test_component_bad_pipe")
+    def bad_pipe(doc):
+        return doc.text
+
+    nlp.add_pipe("test_component_bad_pipe")
+    with pytest.raises(ValueError, match="instead of a Doc"):
+        nlp("text")