I would like to suggest my way to solve this problem. In my mind, it's better to use _init() method for initialization your object if it needs:

package Edge;


use vars qw(%FIELDS);
# Define class properties
use fields qw(from_node to_node label);

{
     # Default values for class properties 
     my $_def_values = { from_node => undef,
                         to_node   => undef,
                         label     => undef,
                       };
     
     sub _class_def { $_def_values; }
}

# Constractor
sub new {
     my $proto = shift;
     my $class = ref($proto) || $proto;      
     
     # Define default values for object instance
     my $defaults = ref($proto) ? $proto : $class->_class_def();   
     my $self = {};
     
     for(keys %$defaults) { $self->{$_} = $defaults->{$_}      }      
+            
     bless $self, $class;      
     $self->_init(@_) if @_;    
     return $self;
}

# Initialization of object
sub _init {
     my $self = shift;
     my %params = @_;
     for my $par(keys %params) {
         $self->{$par} = $params{$par} if exists $FIELDS{$par};
     }
}
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SV* sv_bless(SV* sv, HV* stash);