AssertionError: "Conversion to relational algebra failed to preserve datatypes" when union VARCHAR literal and CAST(null AS INTEGER)

0: jdbc:calcite:model=src/test/resources/mode> select CAST(null AS INTEGER) union select '10';
java.lang.AssertionError: Conversion to relational algebra failed to preserve datatypes:
validated type:
RecordType(VARCHAR NOT NULL EXPR$0) NOT NULL
converted type:
RecordType(VARCHAR EXPR$0) NOT NULL
rel:
LogicalUnion(all=[false])
  LogicalValues(tuples=[[\{ null }]])
  LogicalValues(tuples=[[\{ '10' }]])
 
at org.apache.calcite.sql2rel.SqlToRelConverter.checkConvertedType(SqlToRelConverter.java:487)
at org.apache.calcite.sql2rel.SqlToRelConverter.convertQuery(SqlToRelConverter.java:602)
at org.apache.calcite.prepare.Prepare.prepareSql(Prepare.java:257)
at org.apache.calcite.prepare.Prepare.prepareSql(Prepare.java:220)
at org.apache.calcite.prepare.CalcitePrepareImpl.prepare2_(CalcitePrepareImpl.java:648)
at org.apache.calcite.prepare.CalcitePrepareImpl.prepare_(CalcitePrepareImpl.java:514)
at org.apache.calcite.prepare.CalcitePrepareImpl.prepareSql(CalcitePrepareImpl.java:484)
at org.apache.calcite.jdbc.CalciteConnectionImpl.parseQuery(CalciteConnectionImpl.java:234)
at org.apache.calcite.jdbc.CalciteMetaImpl.prepareAndExecute(CalciteMetaImpl.java:623)
at org.apache.calcite.avatica.AvaticaConnection.prepareAndExecuteInternal(AvaticaConnection.java:674)
at org.apache.calcite.avatica.AvaticaStatement.executeInternal(AvaticaStatement.java:156)
at org.apache.calcite.avatica.AvaticaStatement.execute(AvaticaStatement.java:217)
at sqlline.Commands.executeSingleQuery(Commands.java:1130)
at sqlline.Commands.execute(Commands.java:1079)
at sqlline.Commands.sql(Commands.java:1033)
at sqlline.SqlLine.dispatch(SqlLine.java:822)
at sqlline.SqlLine.begin(SqlLine.java:596)
at sqlline.SqlLine.start(SqlLine.java:269)
at sqlline.SqlLine.main(SqlLine.java:208)