code: def get_ad(variant_call):
      """Gets the allele depth of the VariantCall."""
      return get_format(variant_call, "AD")
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from third_party.nucleus.protos import struct_pb2
  from third_party.nucleus.protos import variants_pb2
  from third_party.nucleus.util import struct_utils
  from third_party.nucleus.util import vcf_constants
label_desc: Use image node_id 4 for calling a global function with example usage: get_ad(variant_call) and returns: get_format