It looks like an issue with JIT. If I disable the JIT then the above query runs successfully.
postgres=# set jit to off;
SET
postgres=# SELECT * FROM rm32044_t1 LEFT JOIN rm32044_t2 ON rm32044_t1.pkey = rm32044_t2.pkey, rm32044_t3 LEFT JOIN rm32044_t4 ON rm32044_t3.pkey = rm32044_t4.pkey order by rm32044_t1.pkey,label,hidden;
The backtrace there is different from the one you posted here in significant ways, but it seems like both that case and this one involve a null pointer showing up for a non-null pass-by-reference datum. That doesn't seem like a whole lot to go on, but maybe somebody who understands the JIT stuff better than I do will have an idea.
