ERROR: could not find pathkey item to sort

ref: 

and

I came across this error/crash when using partitioning of a table with foreign tables (parquet_fdw) as partitions.

It might be an issue with parquet_fdw nothing with postgresql, but I am not able to figure out why it crashes around the sorted option set.

to reproduce,

vijay=# CREATE FOREIGN TABLE example1 (
    one     INT8,
    two     INT8[],
    three   TEXT,
    four    TIMESTAMP,
    five    DATE,
    six     BOOL,
    seven   FLOAT8)
SERVER parquet_srv
OPTIONS (filename '/tmp/parquet_fdw/data/simple/example1.parquet', sorted 'one');

CREATE FOREIGN TABLE example2 (
    one     INT8,
    two     INT8[],
    three   TEXT,
    four    TIMESTAMP,
    five    DATE,
    six     BOOL,
    seven   FLOAT8)
SERVER parquet_srv
OPTIONS (filename '/tmp/parquet_fdw/data/simple/example2.parquet', sorted 'one');
CREATE FOREIGN TABLE
CREATE FOREIGN TABLE
vijay=# select * from example1;
 one |    two     | three |        four         |    five    | six | seven
-----+------------+-------+---------------------+------------+-----+-------
   1 | {1,2,3}    | foo   | 2018-01-01 00:00:00 | 2018-01-01 | t   |   0.5
   2 | {NULL,5,6} | bar   | 2018-01-02 00:00:00 | 2018-01-02 | f   |      
   3 | {7,8,9}    | baz   | 2018-01-03 00:00:00 | 2018-01-03 | t   |     1
   4 | {10,11,12} | uno   | 2018-01-04 00:00:10 | 2018-01-04 | f   |   1.5
   5 | {13,14,15} | dos   | 2018-01-05 00:00:00 | 2018-01-05 | f   |      
   6 | {16,17,18} | tres  | 2018-01-06 00:00:00 | 2018-01-06 | f   |     2
(6 rows)

vijay=# select * from example2;
 one |   two   | three |        four         |    five    | six | seven
-----+---------+-------+---------------------+------------+-----+-------
   1 | {19,20} | eins  | 2018-01-01 00:00:00 | 2018-01-01 | t   |      
   3 | {21,22} | zwei  | 2018-01-03 00:00:00 | 2018-01-03 | f   |      
   5 | {23,24} | drei  | 2018-01-05 00:00:00 | 2018-01-05 | t   |      
   7 | {25,26} | vier  | 2018-01-07 00:00:00 | 2018-01-07 | f   |      
   9 | {27,28} | fünf  | 2018-01-09 00:00:00 | 2018-01-09 | t   |      
(5 rows)

vijay=# create table example (
vijay(#     one     INT8,
vijay(#     two     INT8[],
vijay(#     three   TEXT,
vijay(#     four    TIMESTAMP,
vijay(#     five    DATE,
vijay(#     six     BOOL,
vijay(#     seven   FLOAT8)
vijay-# partition by list(three);
CREATE TABLE
vijay=# alter table example attach partition example1 for values in ('foo', 'bar', 'baz', 'uno', 'dos', 'tres');
ALTER TABLE
vijay=# explain analyze select * from example where three = 'foo';
ERROR:  could not find pathkey item to sort
vijay=# alter table example1 options (drop sorted);
ALTER TABLE
vijay=# alter table example2 options (drop sorted);
ALTER TABLE
vijay=# explain analyze select * from example where three = 'foo';
                                              QUERY PLAN                                              
-------------------------------------------------------------------------------------------------------
 Foreign Scan on example1  (cost=0.00..0.06 rows=1 width=93) (actual time=0.537..0.912 rows=1 loops=1)
   Filter: (three = 'foo'::text)
   Rows Removed by Filter: 5
   Reader: Single File
   Row groups: 1, 2
 Planning Time: 0.888 ms
 Execution Time: 1.399 ms