Redefine type checkers of isnull, isnotnull, and ispresent to IGNORE

Signed-off-by: Yuanchun Shen <yuanchu@amazon.com>

Author: yuancu

core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java

@@ -727,9 +727,7 @@ void populate() {
       registerOperator(SIGNUM, SqlStdOperatorTable.SIGN);
       registerOperator(SIN, SqlStdOperatorTable.SIN);
       registerOperator(CBRT, SqlStdOperatorTable.CBRT);
-      registerOperator(IS_NOT_NULL, SqlStdOperatorTable.IS_NOT_NULL);
-      registerOperator(IS_PRESENT, SqlStdOperatorTable.IS_NOT_NULL);
-      registerOperator(IS_NULL, SqlStdOperatorTable.IS_NULL);
+
       registerOperator(IFNULL, SqlStdOperatorTable.COALESCE);
       registerOperator(EARLIEST, PPLBuiltinOperators.EARLIEST);
       registerOperator(LATEST, PPLBuiltinOperators.LATEST);
@@ -1040,6 +1038,20 @@ void populate() {
                               builder.makeLiteral(" "),
                               arg))),
           PPLTypeChecker.family(SqlTypeFamily.ANY));
+      // Re-define the type checker for is not null, is present, and is null since their original
+      // type checker ANY isn't compatible with struct types.
+      register(
+          IS_NOT_NULL,
+          (builder, args) -> builder.makeCall(SqlStdOperatorTable.IS_NOT_NULL, args),
+          PPLTypeChecker.family(SqlTypeFamily.IGNORE));
+      register(
+          IS_PRESENT,
+          (builder, args) -> builder.makeCall(SqlStdOperatorTable.IS_NOT_NULL, args),
+          PPLTypeChecker.family(SqlTypeFamily.IGNORE));
+      register(
+          IS_NULL,
+          (builder, args) -> builder.makeCall(SqlStdOperatorTable.IS_NULL, args),
+          PPLTypeChecker.family(SqlTypeFamily.IGNORE));
       register(
           LIKE,
           (FunctionImp2)

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalcitePPLConditionBuiltinFunctionIT.java

@@ -24,6 +24,8 @@ public void init() throws Exception {
     loadIndex(Index.STATE_COUNTRY);
     loadIndex(Index.STATE_COUNTRY_WITH_NULL);
     loadIndex(Index.CALCS);
+    loadIndex(Index.NESTED_WITHOUT_ARRAYS);
+    loadIndex(Index.BIG5);
     Request request1 =
         new Request("PUT", "/" + TEST_INDEX_STATE_COUNTRY_WITH_NULL + "/_doc/7?refresh=true");
     request1.setJsonEntity(
@@ -47,6 +49,11 @@ public void testIsNull() throws IOException {
     verifySchema(actual, schema("age", "int"));
 
     verifyDataRows(actual, rows(10));
+
+    // Test isNull on struct objects
+    actual = executeQuery("source=big5 | where isnull(aws) | fields aws");
+    verifySchema(actual, schema("aws", "struct"));
+    verifyNumOfRows(actual, 0);
   }
 
   @Test
@@ -68,6 +75,11 @@ public void testIsNotNull() throws IOException {
         rows("Kevin"),
         rows("    "),
         rows(""));
+
+    // Test isNotNull on struct objects
+    actual = executeQuery("source=big5 | where isnotnull(aws) | fields aws");
+    verifySchema(actual, schema("aws", "struct"));
+    verifyNumOfRows(actual, 1);
   }
 
   @Test