This might be a bigger issue that we need to handle in a separate PR, but based on my reading of the SQLite docs and experimenting with a running PostgreSQL database it appears the the string concat operator (and I think all operators) will return NULL if any of the inputs is null.

From https://www.sqlite.org/lang_expr.html:

The result of any binary operator is either a numeric value or NULL, except for the || concatenation operator,
and the -> and ->> extract operators which evaluate to either NULL or a text value.

All operators generally evaluate to NULL when any operand is NULL, with specific exceptions as stated below.
This is in accordance with the SQL92 standard.

So I guess I would expect sqlc to output nullable types for outputs, but that should perhaps be addressed for all operators in a new PR.

@orisano I didn't mean to imply that we should close this. It might be the correct first step to at least fix the treatment of || to make it equivalent to other binary operators. And then we could create a new issue for nullability of all binary operators. What do you think?