InsertQuery   (children 3)
 Identifier test_null_as_default
 ExpressionList (children 2)
  Identifier a
  Identifier c
 SelectWithUnionQuery (children 1)
  ExpressionList (children 2)
   SelectQuery (children 1)
    ExpressionList (children 2)
     Literal UInt64_1
     Literal NULL
   SelectQuery (children 1)
    ExpressionList (children 2)
     Literal UInt64_2
     Literal NULL
