code: def features_to_string(features):
      if not features:
          return None
      if len(features.key) == 0:
          return None
      return "|".join(
          "%s=%s" % (key, value)
          for key, value in zip(features.key, features.value)
      )
  
imports: from collections import deque
  import subprocess
  from stanza.models.common.utils import misc_to_space_after
  from stanza.models.constituency.parse_tree import Tree
  from stanza.protobuf import DependencyGraph, FlattenedParseTree
  from stanza.server.client import resolve_classpath
label_desc: Use image node_id 9 for calling a global function with example usage: features_to_string(features) and returns: str, None, None