message: Handle NULL while deriving propagation expression
  While constructing the propagation expression in case of queries
  involving default list partitions which have indexes, we ended
  up with NULLs crashing the database.
  Currently, we fallback to planner. But we need to handle it in a
  better way in future.
diff: @@ -564,7 +564,7 @@ CTranslatorExprToDXLUtils::UlPartKeyLevel
  // CTranslatorExprToDXLUtils::PdxlnPartialScanTestRange
  //
  // @doc:
  -// Construct a test expression for the given range
  +// Construct a test expression for the given range or list
  // based part constraint
  //
  //---------------------------------------------------------------------------
  @@ -589,6 +589,17 @@ CTranslatorExprToDXLUtils::PdxlnPartialScanTestRange
  else // list partition
  {
  IDatum *pdatum = prng->PdatumLeft();
  + if (pdatum == NULL)
  + {
  + // TODO: In case of default partitions, we end up with NULL for Left and Right Datum.
  + // Currently we fallback and should handle it better in future.
  + GPOS_RAISE
  + (
  + gpdxl::ExmaDXL,
  + gpdxl::ExmiExpr2DXLUnsupportedFeature,
  + GPOS_WSZ_LIT("Queries over default list partition that have indexes")
  + );
  + }
  GPOS_ASSERT(pdatum->FMatch(prng->PdatumRight()));
  CDXLDatum *pdxldatum = Pdxldatum(pmp, pmda, pdatum);
  