It would make more sense if you were checking the object's error excerpt (i.e. $self->{_error_excerpt}) and not some value you pass to the method. I will have to assume (since you don't show it) that you are calling error_excerpt without any arguments, so it is always undef, and hence you always get "No Error Excerpt".

Something like the following would make more sense:

sub error_excerpt
{
  my $self = shift;
  return defined($self->{_error_excerpt}) ? $self->{_error_excerpt} : 
+"No Error Excerpt.";
}
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