SERVER-62322 Allow an empty object to be projected in $setWindowFieldsserver-62322-setWindowFields-empty-obj

1 files changed, 5 insertions, 2 deletions

diff --git a/src/mongo/db/pipeline/document_source_set_window_fields.cpp b/src/mongo/db/pipeline/document_source_set_window_fields.cpp
index 87cd3ad0267..09e27df140a 100644
--- a/src/mongo/db/pipeline/document_source_set_window_fields.cpp
+++ b/src/mongo/db/pipeline/document_source_set_window_fields.cpp
@@ -461,10 +461,12 @@ DocumentSource::GetNextResult DocumentSourceInternalSetWindowFields::doGetNext()
     MutableDocument addFieldsSpec;
     for (auto&& [fieldName, function] : _executableOutputs) {
         try {
+            // Wrap the projected value in a $literal since there are limitations on a user-facing
+            // $addFields that we don't want to enforce here (e.g. empty object).
+            addFieldsSpec.addField(fieldName, Value(DOC("$literal" << function->getNext())));
+        } catch (const DBException&) {
             // If we hit a uassert while evaluating expressions on user data, delete the temporary
             // table before aborting the operation.
-            addFieldsSpec.addField(fieldName, function->getNext());
-        } catch (const DBException&) {
             _iterator.finalize();
             throw;
         }
@@ -506,6 +508,7 @@ DocumentSource::GetNextResult DocumentSourceInternalSetWindowFields::doGetNext()
             _iterator.finalize();
             break;
     }
+
     auto projExec = projection_executor::AddFieldsProjectionExecutor::create(
         pExpCtx, addFieldsSpec.freeze().toBson());