Decimal data serialized as Double in Protocol Buffer API

[employee@centos7-ws test]$ protoc --decode_raw < test.pb
1: "org.apache.calcite.avatica.proto.Responses$ExecuteResponse"
2 {
  1 {
    1: "cf74c4e9-29bc-410a-b557-bf7a4965cbaf"
    2: 479389
    3: 1
    4 {
      1 {
        4: 1
        8: 255
        9: "KEYCOLUMN"
        10: "KEYCOLUMN"
        12: 255
        14: "DECIMAL_TABLE_38_6"
        16: 1
        19: "java.lang.String"
        20 {
          1: 12
          2: "VARCHAR"
          3: 21
        }
      }
      1 {
        1: 1
        4: 1
        6: 1
        7: 1
        8: 38
        9: "COLUMN1"
        10: "COLUMN1"
        12: 38
        13: 6
        14: "DECIMAL_TABLE_38_6"
        16: 1
        19: "java.math.BigDecimal"
        20 {
          1: 3
          2: "DECIMAL"
          3: 23
        }
      }
      2: "select * from decimal_table_38_6"
      4 {
        1: 4
      }
    }
    5 {
      2: 1
      3 {
        1 {
          1 {
            1: 21
            3: "ConversionTestKey"
          }
        }
        1 {
          1 {
            1: 22
            6: 0x3ffe666666666666
          }
        }
      }
      3 {
        1 {
          1 {
            1: 21
            3: "FractionalNumeric6"
          }
        }
        1 {
          1 {
            1: 22
            6: 0x40ba0a524af0bf1a
          }
        }
      }
      3 {
        1 {
          1 {
            1: 21
            3: "FractionalNumeric8"
          }
        }
        1 {
          1 {
            1: 22
            6: 0xbff1f9acffa7eb6c
          }
        }
      }
      3 {
        1 {
          1 {
            1: 21
            3: "Null"
          }
        }
        1 {
          1 {
            1: 24
          }
        }
      }
      3 {
        1 {
          1 {
            1: 21
            3: "OnePlusFraction"
          }
        }
        1 {
          1 {
            1: 22
            6: 0x3ff000010c6f7a0b
          }
        }
      }
    }
    6: 18446744073709551615
    7 {
      1: "centos7-ws:8765"
    }
  }
  3 {
    1: "centos7-ws:8765"
  }
}