Recursive CTE and collation

Hi,

While playing with the query showed here :
https://fluca1978.github.io/2019/06/12/PartitioningCTE.html

I've seen something strange with v12 (actually compiled after
f43608bda2111a1fda514d1bed4df313ee2bbec3 so more recent than beta1) :

psql: ERROR:  recursive query "inheritance_tree" column 3 has collation
"default" in non-recursive term but collation "C" overall
LINE 4:             , NULL::text AS table_parent_name
                      ^
HINT:  Use the COLLATE clause to set the collation of the non-recursive
term.

It work correctly with 11, and with 12, we can workaround by adding
COLLATE "C" after NULL::text, so I don't know if it's a bug or a new
feature, but it break things, at least.

The database I use is created with en_US collation :

testpart=# \l
 testpart  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |

testpart=# show lc_collate ;
 lc_collate 
-------------
 en_US.UTF-8

regards,

--

Sébastien