NullpointerExceptions in dataset processing when target cannot be found.

[joaquinvanschoren]

Some datasets fail during processing. They all fail with a NullpointerException that occurs while setting the target feature.

Checking the datasets (uploaded by Guillaume), they have a feature such as:
@Attribute "Is Public Domain" {True, False}
while in the database this is stored as 'Is_Public_Domain'.
I assume the underscores are added during dataset upload.

What is more troubling is that there seems to be no trace of this error. The message says that the error is marked in the database but I could not find it. I assume it tries to store an error message but that fails, too?

[23-12-2018 23:23:43] [OK] [Process Dataset] Processing dataset 41249 - obtaining features.
java.lang.NullPointerException
	at weka.core.Instances.setClass(Instances.java:1532)
	at org.openml.webapplication.features.ExtractFeatures.getFeatures(ExtractFeatures.java:42)
	at org.openml.webapplication.ProcessDataset.process(ProcessDataset.java:65)
	at org.openml.webapplication.ProcessDataset.<init>(ProcessDataset.java:41)
	at org.openml.webapplication.Main.main(Main.java:120)
[23-12-2018 23:23:43] [Error] [Process Dataset] Error while processing dataset. Marking this in database.
[23-12-2018 23:23:43] [Error] [Process Dataset] Dataset 41249 - Error: null