calcite variable $cor0 is not found

[you Zhuang]

String sql = "select id, name, (select id from test.users where id = b.id)
as pid from test.depts b";

sqlToRelConverter.convertQuery(validatedSqlNode, false, true)

i can get the following

[main:DEBUG] org.apache.calcite.sql2rel: Plan after converting SqlNode to
RelNode
LogicalProject(ID=[$0], NAME=[$1], PID=[$SCALAR_QUERY({
LogicalProject(ID=[$0])
  LogicalFilter(condition=[=($0, $cor0.id)])
    LogicalTableScan(table=[[test, users]])
})])
  LogicalTableScan(table=[[test, depts]])


but when i execute code:

sqlNode = new RelToSqlConverter(SPARK).visitRoot(rel)

it throws the exception: variable $cor0 is not found

is it a bug issue?