code: private static Schema getActualRecord(Schema inputSchema) {
      if (Type.RECORD.equals(inputSchema.getType())) {
        return inputSchema;
      }
  
      Preconditions.checkArgument(Type.UNION.equals(inputSchema.getType()), "Nested schema is only support with either record or union type of null with record");
      Preconditions.checkArgument(inputSchema.getTypes().size() <= 2,
          "For union type in nested record, it should only have NULL and Record type");
  
      for (Schema inner : inputSchema.getTypes()) {
        if (Type.NULL.equals(inner.getType())) {
          continue;
        }
        Preconditions.checkArgument(Type.RECORD.equals(inner.getType()), "For union type in nested record, it should only have NULL and Record type");
        return inner;
  
      }
      throw new IllegalArgumentException(inputSchema + " is not supported.");
    }
docs: For the schema that is a UNION type with NULL and Record type, it provides Records type.
  @param inputSchema
  @return