code: public static Schema fieldSchema(Schema schema, PartitionStrategy strategy,
                                     String name) {
      if (strategy != null && Accessor.getDefault().hasPartitioner(strategy, name)) {
        return partitionFieldSchema(Accessor.getDefault().getPartitioner(strategy, name),
            schema);
      }
      Schema nested = fieldSchema(schema, name);
      if (nested != null) {
        return nested;
      }
      throw new IllegalArgumentException(
          "Not a schema or partition field: " + name);
    }
docs: Returns a {@link Schema} for the given field name, which could be either a
  schema field or a partition field.
  
  @param schema an entity Schema that will be partitioned
  @param strategy a {@code PartitionStrategy} used to partition entities
  @param name a schema or partition field name
  @return a Schema for the partition or schema field