Computed field error messages when referencing cck fields that are not "Required fields"

Thanks for all the work on Computed Field. As you say, really powerful.

I do get error reports when doing some chemistry with Computed Field. The following works just fine in a computed field where a function in a custom module is accessing and processing data contained in some other cck fields.

$atomproperty = atoms ("atomnumbers", 
$entity->field_group_1['und'][0]['value'] , 
$entity->field_group_1_number['und'][0]['value'] , 
$entity->field_group_2['und'][0]['value'] , 
$entity->field_group_2_number['und'][0]['value'] );

However this throws a number of identical errors on previewing and saving a node, all of which are

Notice: Undefined offset: 0 in eval() (line 1 of /...path.../drupal7/sites/all/modules/computed_field/computed_field.module(401) : eval()'d code).

This seems related to the situation where field_group_1, field_group_1_number, and so on, are not required fields, quite properly from a science point of view. The calculation works just fine despite the error messages. If all field_group_1 and so on contain data, there are no error messages.

As a workaround I can work eliminate the messages by making the fields required, making zero or none the default values, and then making sure I ignore those values in my function. However I suspect that, in general, the user should be able to allow cck fields referenced from a computed field to be empty when it makes sense for that to be the case. Therefore would it be possible please for the Computed Field module not to report an error when there are no entries in cck fields that a formula in a Computed Field module requires. Or if I am missing a point somewhere please advise. Many thanks.