sumIf(Nullable()) and similar unary functions (unary w/o If combinator)
was working incorrectly, since it returns "sum" from the getName()
helper, and so distributed query processing fails.
The problem is in the optimization in
AggregateFunctionIfNullUnary::add() for the unary functions. It pass
only one column to write result to, instead of all passed arguments +
result columns.
While AggregateFunctionIf::add() assumes that it accepts arguments +
result columns, and use last column as a result.
Introduced-in: #16610Fixes: #18210
