Recoverable fatal error: Argument 2 passed to drupal_array_get_nested_value() must be an array, null given

It seems to be possible to save Email field with a value such as "-" which is obviously an invalid email, a bug in itself.

However if you save the Email with this value, when you then go to resave / update that content and leave the email as "-", you get the error:

Recoverable fatal error: Argument 2 passed to drupal_array_get_nested_value() must be an array, null given, called in modules/field/field.form.inc on line 365 and defined in drupal_array_get_nested_value() (line 6348 of includes/common.inc).