SERVER-63008 [SBE] Return an empty array when $concatArrays has no children

2 files changed, 3 insertions, 4 deletions

diff --git a/jstests/aggregation/bugs/server14872.js b/jstests/aggregation/bugs/server14872.js
index f3e4abf85b6..8c0751a8e23 100644
--- a/jstests/aggregation/bugs/server14872.js
+++ b/jstests/aggregation/bugs/server14872.js
@@ -23,10 +23,6 @@ assert.eq(coll.aggregate(pipeline).toArray(), [{all: [1, 2, [3], 4]}]);
 pipeline = [{$project: {_id: 0, all: {$concatArrays: ['$a']}}}];
 assert.eq(coll.aggregate(pipeline).toArray(), [{all: [1, 2]}]);
 
-// Concatenation with no arguments.
-pipeline = [{$project: {_id: 0, all: {$concatArrays: []}}}];
-assert.eq(coll.aggregate(pipeline).toArray(), [{all: []}]);
-
 // Any nullish inputs will result in null.
 pipeline = [{$project: {_id: 0, all: {$concatArrays: ['$a', '$e']}}}];
 assert.eq(coll.aggregate(pipeline).toArray(), [{all: null}]);
diff --git a/jstests/aggregation/expressions/concat_arrays.js b/jstests/aggregation/expressions/concat_arrays.js
index f4bf2241d0f..351d36dccf7 100644
--- a/jstests/aggregation/expressions/concat_arrays.js
+++ b/jstests/aggregation/expressions/concat_arrays.js
@@ -87,6 +87,9 @@ runAndAssert(
     ["$str_arr", {$filter: {input: [], cond: {$isArray: [{$concatArrays: [[], "$$this"]}]}}}],
     [["a", "b", "c"]]);
 
+// Concatenation with no arguments results in the empty array.
+runAndAssert([], [[]]);
+
 // Confirm that having any combination of null or missing inputs and valid inputs produces null.
 runAndAssertNull(["$int_arr", "$null_val"]);
 runAndAssertNull(["$int_arr", null]);