"Strict warning: Only variables should be passed by reference in eval()" when concatenating several text fields
$entity_field[0]['value'] = array_pop(array_pop(field_get_items($entity_type, $entity, 'field_address')));


=>

$items = array_pop(field_get_items($entity_type, $entity, 'field_address'));
$entity_field[0]['value'] = array_pop($items);


You have to store result of function in variable and pass it to another function, instead of pass function to function.

Passing by Reference