code: @Nullable
    private static DimFilter toExpressionLeafFilter(
        final PlannerContext plannerContext,
        final RowSignature rowSignature,
        final RexNode rexNode
    )
    {
      final DruidExpression druidExpression = toDruidExpression(plannerContext, rowSignature, rexNode);
      return druidExpression != null
             ? new ExpressionDimFilter(druidExpression.getExpression(), plannerContext.getExprMacroTable())
             : null;
    }
docs: Translates to an "expression" type leaf filter. Used as a fallback if we can't use a simple leaf filter.