Undefined index: fields field.info.inc:596

We are using static cache in this function, which on line foreach (field_info_bundles() as $entity_type => $bundles) { gets cleared so the $info array has no $info['fields'] key.
The backtrace shows this chain:

->_field_info_collate_fields(FALSE)
->field_info_bundles()
->field_info_bundles
->entity_get_info
->drupal_alter
->entity_entity_info_alter
->_field_info_collate_fields(TRUE).

While this is a notice, I've left it on normal priority because we lose the half of the returned array. :)
Related issues:
#1040790: _field_info_collate_fields() memory usage
#1759614: Undefined index: fields field.info.inc:596