If() formula can't return null value

[Nicklas Nordborg]

Create an 'Intensity expression' formula with for example:

if(raw('status') == 'HIDATA', null, raw('fpkm'))

Eg. it should return null if status is HIDATA, otherwise the 'fpkm' value.

Error message when creating a root bioassay set:

13:35:01,748 ERROR InternalJobQueue:585 - Exception while executing job: Job[id=633834; name=Create root bioassay set in experiment 'New experiment' using formula 'FPKM (null hidata)']
net.sf.basedb.core.BaseException: Invalid use of null. The 'value' value cannot be set to null.
	at net.sf.basedb.core.InternalJobQueue$JobRunner.run(InternalJobQueue.java:579)
	at java.lang.Thread.run(Unknown Source)
Caused by: net.sf.basedb.core.InvalidUseOfNullException: Invalid use of null. The 'value' value cannot be set to null.
	at net.sf.basedb.core.query.WhenStatement.<init>(WhenStatement.java:52)
	at net.sf.basedb.util.jep.convert.IfConverter.toExpression(IfConverter.java:78)
	at net.sf.basedb.util.jep.convert.IfConverter.toExpression(IfConverter.java:40)
	at net.sf.basedb.util.jep.convert.ASTFunNodeConverter.toExpression(ASTFunNodeConverter.java:83)
	at net.sf.basedb.util.jep.convert.ASTFunNodeConverter.toExpression(ASTFunNodeConverter.java:43)
	at net.sf.basedb.util.jep.Jep.nodeToExpression(Jep.java:295)
	at net.sf.basedb.util.jep.Jep.jepToExpression(Jep.java:223)
	at net.sf.basedb.util.jep.Jep.formulaToExpression(Jep.java:234)
	at net.sf.basedb.util.IntensityCalculatorUtil.createJepExpressions(IntensityCalculatorUtil.java:504)
	at net.sf.basedb.plugins.IntensityCalculatorPlugin.run(IntensityCalculatorPlugin.java:240)
	at net.sf.basedb.core.PluginExecutionRequest.invoke(PluginExecutionRequest.java:116)
	at net.sf.basedb.core.InternalJobQueue$JobRunner.run(InternalJobQueue.java:571)
	... 1 more

[Nicklas Nordborg]

(In [6557]) Fixes #1862: If() formula can't return null value