Submitted by: @dyemanov

Is related to QA391

Test case:

execute block (i varchar(10) = :a) returns (o varchar(10))
as
begin
o = coalesce(cast(o as date), current_date);
o = i;
suspend;
end

If called with an input parameter e.g. 'asd', it throws a conversion error instead of returning 'asd'.

The problem is caused by a hidden variable overwriting the output parameter node, as they mistakenly share the same BLR variable identifier.

Commits: 28aa57f