The call on Mage_Eav_Model_Attribute_Data_Text:67 to empty returns true of a value of "0" is entered, as specified in the PHP spec. This prevents the entry of zero on the backend admin for fields. Zero should be a valid value, as it was in our case.

No unit tests were created, as no unit tests exist currently for the Eav module.

Sorry for not including this originally.

The line was
if($previusInvoice->getShippingAmount() && ...
This would return true if a previous invoice had zero shipping because it was returned as a string from the database. The string "0.0000". The line needs to be changed to have a greaterthan comparison to cause the string to cast to a numeric.

Also added unit test.

The line was
if($previusInvoice->getShippingAmount() && ...
This would return true if a previous invoice had zero shipping because it was returned as a string from the database. The string "0.0000". The line needs to be changed to have a greaterthan comparison to cause the string to cast to a numeric.

Also added unit test.

Added comments