The filenames of CorDapps that are installed in the node are not saved to the database. Currently, they are saved as `null`. Ideally, the filename should be read and persisted into the filename column.
Assuming getting the filename is simple, the difficulty of this task comes from correcting the filenames of CorDapps in existing nodes. One potential solution, is to read the attachments out of the database, compare their hash's to those of the CorDapps in the node, take the filename from the matching CorDapps and update the records in the database.
This should fix CorDapps that live in the `cordapps` directory but will not fix any old CorDapps that have been received over the network or legacy versions that no longer live in the `cordapps` directory.