code: public static Schema mapOf(Schema keySchema, Schema valueSchema) {
      return new Schema(Type.MAP, null, null, keySchema, valueSchema, null, null, null);
    }
docs: Creates a {@link Type#MAP MAP} {@link Schema} of the given key and value types.
  @param keySchema Schema of the map key.
  @param valueSchema Schema of the map value
  @return A {@link Schema} of {@link Type#MAP MAP} type.