fix(NODE-1843): bulk operations ignoring provided sessions [PORT] (#2898)

Author: nbbeeken

lib/bulk/common.js

@@ -1176,8 +1176,11 @@ class BulkOperationBase {
    * @param {function} callback
    */
   bulkExecute(_writeConcern, options, callback) {
-    if (typeof options === 'function') (callback = options), (options = {});
-    options = options || {};
+    if (typeof options === 'function') {
+      callback = options;
+    }
+
+    const finalOptions = Object.assign({}, this.s.options, options);
 
     if (typeof _writeConcern === 'function') {
       callback = _writeConcern;
@@ -1203,7 +1206,7 @@ class BulkOperationBase {
       const emptyBatchError = toError('Invalid Operation, no operations specified');
       return this._handleEarlyError(emptyBatchError, callback);
     }
-    return { options, callback };
+    return { options: finalOptions, callback };
   }
 
   /**