NullPointerException when validating a derived bioassay without a subtype

[Nicklas Nordborg]

Create a derived bioassay without a subtype. Then go to the 'Overview' tab and click on 'Validate'. This results in a NullPointerException.

java.lang.NullPointerException
...at net.sf.basedb.util.overview.validator.DataFileValidator.postValidateFolder(DataFileValidator.java:257)
...at net.sf.basedb.util.overview.node.NodeFactory.postValidateFolder(NodeFactory.java:222)
...at net.sf.basedb.util.overview.loader.BasicItemNodeLoader.postValidateFolder(BasicItemNodeLoader.java:132)
...at net.sf.basedb.util.overview.loader.DataFileLoader.createPropertyNode(DataFileLoader.java:88)
...at net.sf.basedb.util.overview.loader.AutoChildNodeLoader.createPropertyNode(AutoChildNodeLoader.java:81)
...at net.sf.basedb.util.overview.loader.DerivedBioAssayLoader.loadPropertyChildNodes(DerivedBioAssayLoader.java:136)
...at net.sf.basedb.util.overview.loader.AbstractNodeLoader.loadChildNodesOfItemNode(AbstractNodeLoader.java:125)
...at net.sf.basedb.util.overview.loader.AbstractNodeLoader.loadChildNodes(AbstractNodeLoader.java:110)

[Nicklas Nordborg]

(In [6089]) Fixes #1710: NullPointerException when validating a derived bioassay without a subtype