[fix](be) Fix concat_ws nullable array handling

be/src/exprs/function/function_string_concat.h

@@ -417,6 +417,11 @@ class FunctionStringConcatWs : public IFunction {
         std::vector<std::string_view> views;
 
         if (is_column<ColumnArray>(argument_columns[1].get())) {
+            if (argument_size != 2) {
+                return Status::InvalidArgument(
+                        "concat_ws with array argument expects exactly 2 arguments, but got {}",
+                        argument_size);
+            }
             // Determine if the nested type of the array is String
             const auto& array_column = reinterpret_cast<const ColumnArray&>(*argument_columns[1]);
             if (!array_column.get_data().is_column_string()) {
@@ -472,6 +477,7 @@ class FunctionStringConcatWs : public IFunction {
         const auto& src_string_offsets = string_column.get_offsets();
         const auto& src_array_offsets = array_column.get_offsets();
         size_t current_src_array_offset = 0;
+        auto& array_nullmap = *null_list[1];
 
         // Concat string in array
         for (size_t i = 0; i < input_rows_count; ++i) {
@@ -485,6 +491,12 @@ class FunctionStringConcatWs : public IFunction {
                 continue;
             }
 
+            if (array_nullmap[i]) {
+                StringOP::push_empty_string(i, res_data, res_offset);
+                current_src_array_offset += src_array_offsets[i] - src_array_offsets[i - 1];
+                continue;
+            }
+
             int sep_size = sep_offsets[i] - sep_offsets[i - 1];
             const char* sep_data = reinterpret_cast<const char*>(&sep_chars[sep_offsets[i - 1]]);
 

regression-test/data/nereids_function_p0/scalar_function/concat_ws.out

@@ -37,3 +37,10 @@ a-b-css-d
 x-y-z
 你好-世界-Doris-Nereids
 
+-- !concat_ws_array_null_full --
+1	[]	0
+2	[a,b,c]	5
+
+-- !concat_ws_array_null_filter --
+1	[]	0
+

regression-test/suites/nereids_function_p0/scalar_function/concat_ws.groovy

@@ -39,4 +39,17 @@ suite("nereids_scalar_fn_concat_ws") {
     sql "INSERT INTO test_concat_ws_1 VALUES (1, ['a','b'], ['css',null,'d']), (2, ['x',null], ['y','z']),(3,['你好','世界'],['Doris',null,'Nereids'])"
     qt_concat_ws_insert_1 "SELECT concat_ws('-', a, b) FROM test_concat_ws_1 ORDER BY id"
 
-}
+    sql "DROP TABLE IF EXISTS test_concat_ws_array_null"
+    sql "CREATE TABLE test_concat_ws_array_null (id INT, a ARRAY<VARCHAR>, b ARRAY<VARCHAR>, c ARRAY<VARCHAR>) ENGINE=OLAP DISTRIBUTED BY HASH(id) BUCKETS 1 PROPERTIES ('replication_num' = '1')"
+    sql "INSERT INTO test_concat_ws_array_null VALUES (1, ['a'], NULL, ['b']), (2, ['a'], ['b'], ['c'])"
+    qt_concat_ws_array_null_full "SELECT id, CONCAT('[', CONCAT_WS(',', a, b, c), ']'), LENGTH(CONCAT_WS(',', a, b, c)) FROM test_concat_ws_array_null ORDER BY id"
+    qt_concat_ws_array_null_filter "SELECT id, CONCAT('[', CONCAT_WS(',', a, b, c), ']'), LENGTH(CONCAT_WS(',', a, b, c)) FROM test_concat_ws_array_null WHERE id = 1"
+
+    sql "SET disable_nereids_expression_rules = 'CONCATWS_MULTI_ARRAY_TO_ONE'"
+    test {
+        sql "SELECT CONCAT_WS(',', a, b, c) FROM test_concat_ws_array_null ORDER BY id"
+        exception "concat_ws with array argument expects exactly 2 arguments"
+    }
+    sql "SET disable_nereids_expression_rules = ''"
+
+}