my $obj = MyClass->new();  # what if it returns undef on error?
if ($obj->can('top')       # dies!

##</code><code>##

# Instead of:
    if (UNIVERSAL::isa($obj, 'MyClass')
# do this:
    if (blessed $obj  &&  $obj->isa('MyClass'))

# Instead of:
    if (UNIVERSAL::can($obj, 'top')
    &&  UNIVERSAL::can($obj->top, 'bottom'))
# do this:
    if (blessed $obj && $obj->can('top')
    &&  blessed $obj->top && $obj->top->can('bottom'))