Its likely your connect() is failing. You should be checking the status of your connect like so:

# Some possibilities
my $dbh = DBI->connect(..., {RaiseError=>1});
or
my $dbh = DBI->connect(...) or die $DBI::errstr;
or
my $dbh = eval { DBI->connect(..., {RaiseError}=>1) };
redirect_to_some_friendly_page_that_says_our_database_is_down($@) if $
+@;
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