2.2.7: JUEL's ${not x} fails with NPE if using custom typeConverter which returns null

[oxygenecore]

If I override TypeConverterImpl in a manner to return null for input null values (to imitate apache's COERCE_TO_ZERO=false), ${not x} fails with NPE:

java.lang.NullPointerException
at de.odysseus.el.tree.impl.ast.AstUnary$3.apply(AstUnary.java:46)
at de.odysseus.el.tree.impl.ast.AstUnary$SimpleOperator.eval(AstUnary.java:32)
at de.odysseus.el.tree.impl.ast.AstUnary.eval(AstUnary.java:64)
at de.odysseus.el.tree.impl.ast.AstEval.eval(AstEval.java:51)
at de.odysseus.el.tree.impl.ast.AstNode.getValue(AstNode.java:31)
at de.odysseus.el.TreeValueExpression.getValue(TreeValueExpression.java:122)

Also, it seems that math binary operations also do not work with nulls properly - if one of parameters is null and other is not, code proceeds to an actual math block with implicit casts to a primitive number.