1 files changed, 2 insertions, 6 deletions
diff --git a/src/mongo/db/pipeline/document_source_group.h b/src/mongo/db/pipeline/document_source_group.h
index 72fd2832bf1..edffed6758b 100644
--- a/src/mongo/db/pipeline/document_source_group.h
+++ b/src/mongo/db/pipeline/document_source_group.h
@@ -145,9 +145,7 @@ public:
     /**
      * Returns the expression to use to determine the group id of each document.
      */
-    const boost::intrusive_ptr<Expression> getIdExpression() const {
-        return _idExpression;
-    }
+    boost::intrusive_ptr<Expression> getIdExpression() const;
 
     /**
      * Returns true if this $group stage represents a 'global' $group which is merging together
@@ -284,13 +282,11 @@ private:
 
     std::shared_ptr<Sorter<Value, Value>::File> _file;
 
-    // The expression for the '_id' field.
-    boost::intrusive_ptr<Expression> _idExpression;
     // If the expression for the '_id' field represents a non-empty object, we track its fields'
     // names in '_idFieldNames'.
     std::vector<std::string> _idFieldNames;
     // Expressions for the individual fields when '_id' produces a document in the order of
-    // '_idFieldNames' or the whole expression if '_id' produces a scalar value.
+    // '_idFieldNames' or the whole expression otherwise.
     std::vector<boost::intrusive_ptr<Expression>> _idExpressions;
 
     bool _initialized;