Ensure updates aren't made if no gold available

spacy/gold.pyx

@@ -406,11 +406,11 @@ cdef class GoldParse:
         if tags is None:
             tags = [None for _ in doc]
         if heads is None:
-            heads = [token.i for token in doc]
+            heads = [None for token in doc]
         if deps is None:
             deps = [None for _ in doc]
         if entities is None:
-            entities = ['-' for _ in doc]
+            entities = [None for _ in doc]
         elif len(entities) == 0:
             entities = ['O' for _ in doc]
         elif not isinstance(entities[0], basestring):

spacy/syntax/ner.pyx

@@ -113,7 +113,7 @@ cdef class BiluoPushDown(TransitionSystem):
 
     def has_gold(self, GoldParse gold, start=0, end=None):
         end = end or len(gold.ner)
-        if all([tag == '-' for tag in gold.ner[start:end]]):
+        if all([tag in ('-', None) for tag in gold.ner[start:end]]):
             return False
         else:
             return True

spacy/syntax/nn_parser.pyx

@@ -483,6 +483,9 @@ cdef class Parser:
         return beams
 
     def update(self, docs_tokvecs, golds, drop=0., sgd=None, losses=None):
+        docs_tokvecs, golds = self._filter_unlabelled(docs_tokvecs, golds)
+        if not golds:
+            return None
         if self.cfg.get('beam_width', 1) >= 2 and numpy.random.random() >= 0.5:
             return self.update_beam(docs_tokvecs, golds,
                     self.cfg['beam_width'], self.cfg['beam_density'],
@@ -555,6 +558,9 @@ cdef class Parser:
 
     def update_beam(self, docs_tokvecs, golds, width=None, density=None,
             drop=0., sgd=None, losses=None):
+        docs_tokvecs, golds = self._filter_unlabelled(docs_tokvecs, golds)
+        if not golds:
+            return None
         if width is None:
             width = self.cfg.get('beam_width', 2)
         if density is None:
@@ -605,6 +611,15 @@ cdef class Parser:
             bp_my_tokvecs(d_tokvecs, sgd=sgd)
         return d_tokvecs
 
+    def _filter_unlabelled(self, docs_tokvecs, golds):
+        '''Remove inputs that have no relevant labels before update'''
+        has_golds = [self.moves.has_gold(gold) for gold in golds]
+        docs, tokvecs = docs_tokvecs
+        docs = [docs[i] for i, has_gold in enumerate(has_golds) if has_gold]
+        tokvecs = [tokvecs[i] for i, has_gold in enumerate(has_golds) if has_gold]
+        golds = [golds[i] for i, has_gold in enumerate(has_golds) if has_gold]
+        return (docs, tokvecs), golds
+
     def _init_gold_batch(self, whole_docs, whole_golds):
         """Make a square batch, of length equal to the shortest doc. A long
         doc will get multiple states. Let's say we have a doc of length 2*N,