code: public static boolean isField(Schema schema, PartitionStrategy strategy,
                                  String name) {
      Schema.Field field = schema.getField(name);
      return ((field != null) ||
          (strategy != null && Accessor.getDefault().hasPartitioner(strategy, name)));
    }
docs: Return whether there is a field named {@code name} in the schema or
  partition strategy.
  
  @param schema a {@code Schema}
  @param strategy a {@code PartitionStrategy}
  @param name a String field name
  @return {@code true} if {@code name} identifies a field