sub dt_from_string {
my ( $date_string, $date_format, $tz ) = @_;
return if $date_string and $date_string =~ m|^0000-0|;
return undef if $date_string and $date_string =~ m|^0000-0|;
my $do_fallback = defined($date_format) ? 0 : 1;
my $server_tz = C4::Context->tz;
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