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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _serialize(self, entity, pb, prefix='', parent_repeated=False, projection=None):
 """Internal helper to serialize this property to a protocol buffer. Subclasses may override this method. Args: entity: The entity, a Model (subclass) instance. pb: The protocol buffer, an EntityProto instance. prefix: Optional name prefix used for StructuredProperty (if present, must end in '.'). parent_repeated: True if the parent (or an earlier ancestor) is a repeated Property. projection: A list or tuple of strings representing the projection for the model instance, or None if the instance is not a projection. """

    values = self._get_base_value_unwrapped_as_list(entity)
    name = prefix + self._name
    if projection and name not in projection:
      return

    if self._indexed:
      create_prop = lambda: pb.add_property()
    else:
      create_prop = lambda: pb.add_raw_property()

    if self._repeated and not values and self._write_empty_list:
      # We want to write the empty list
      p = create_prop()
      p.set_name(name)
      p.set_multiple(False)
      p.set_meaning(entity_pb.Property.EMPTY_LIST)
      p.mutable_value()
    else:
      # We write a list, or a single property
      for val in values:
        p = create_prop()
        p.set_name(name)
        p.set_multiple(self._repeated or parent_repeated)
        v = p.mutable_value()
        if val is not None:
          self._db_set_value(v, p, val)
          if projection:
            # Projected properties have the INDEX_VALUE meaning and only contain
            # the original property's name and value.
            new_p = entity_pb.Property()
            new_p.set_name(p.name())
            new_p.set_meaning(entity_pb.Property.INDEX_VALUE)
            new_p.set_multiple(False)
            new_p.mutable_value().CopyFrom(v)
            p.CopyFrom(new_p)