Importer: reading undefined array index with 'is_null()'

[Offereins]

While importing a phpBB forum with version 2.5.4 the following error appears repeatedly:

Notice: Undefined index: to_fieldname in \wp-content\plugins\bbpress\includes\admin\converter.php on line 898

I'm not sure if this is related to the fact that, previous to this point, I removed all plugin data with a bbPress reset, as well as that the import was interrupted and restarted with a purge.

Guessing this is probably not phpBB related, so suggested is to check the array value with isset() and replace the ! is_null() check, since isset() also returns false when the value equals to null. Patch for trunk attached.

[Offereins]

Replace is_null with isset

[thebrandonallen]

Good catch @Offereins! Adding fresh patch against trunk.

[netweb]

In 6041:

Importers: In BBP_Converter_Base::convert_table() method use isset() rather than ! is_null

Props Offereins
Fixes #2733