void nvl2(HplsqlParser.Expr_func_paramsContext ctx) {
    if (ctx.func_param().size() == 3) {
      Var firstParam = evalPop(ctx.func_param(0).expr());
      if (!firstParam.isNull()) {
        eval(ctx.func_param(1).expr());
      }
      else {
        eval(ctx.func_param(2).expr());
      }
    }
    else {
      evalNull();
    }
  }
NVL2 function - If expr1 is not NULL return expr2, otherwise expr3
hplsql/src/main/java/org/apache/hive/hplsql/functions/FunctionMisc.java