Evaluation of the WHERE ... IN ... with multiple columns 

In the case that there is a flattenable subselect with multiple columns, the RowConstructorNode was passed along, and it crashed at the ASTLoader. The fix handles this issue. It builds a branch with AndNodes with on the left side an BinaryComparisonOperatorNode and at the end a Boolean True.  

Extra checks prevent unsupported (and unpredictable) evaluation of cases where a different number of columns are present in the left and right side of the  ... IN ... operator. 
Why does the right hand side call getExpression, but the left hand does not?