Fix bug when docs are empty

spacy/pipeline.pyx

@@ -447,6 +447,9 @@ class Tagger(Pipe):
             yield from docs
 
     def predict(self, docs):
+        if not any(len(doc) for doc in docs):
+            # Handle case where there are no tokens in any docs.
+            return [self.model.ops.allocate((0, self.model.nO) for doc in docs]
         tokvecs = self.model.tok2vec(docs)
         scores = self.model.softmax(tokvecs)
         guesses = []