code: public static Schema fieldSchema(Schema schema, String name) {
      Schema nested = unwrapNullable(schema);
      List<String> levels = Lists.newArrayList();
      for (String level : NAME_SPLITTER.split(name)) {
        levels.add(level);
        ValidationException.check(Schema.Type.RECORD == schema.getType(),
            "Cannot get schema for %s: %s is not a record schema: %s",
            name, NAME_JOINER.join(levels), nested.toString(true));
        Schema.Field field = nested.getField(level);
        ValidationException.check(field != null,
            "Cannot get schema for %s: %s is not a field",
            name, NAME_JOINER.join(levels));
        nested = unwrapNullable(field.schema());
      }
      return nested;
    }
docs: Returns the nested {@link Schema} for the given field name.
  
  @param schema a record Schema
  @param name a String field name
  @return the nested Schema for the field