value could be a string, not always a numeric

modules/Bio/EnsEMBL/DBSQL/AttributeAdaptor.pm

@@ -165,7 +165,7 @@ sub store_on_ {
             "argument expected.");
     }
 
-    next if ($attrib->value == 0);
+    next if ($attrib->value eq '0');
 
     my $atid = $self->_store_type( $attrib );
     if ((defined $attrib->code) and ($attrib->code eq 'circular_seq')) {