1 files changed, 58 insertions, 0 deletions
diff --git a/jstests/aggregation/bugs/server6131.js b/jstests/aggregation/bugs/server6131.js
new file mode 100644
index 00000000000..10ac4d28997
--- /dev/null
+++ b/jstests/aggregation/bugs/server6131.js
@@ -0,0 +1,58 @@
+// $unwind applied to an empty array field drops the field from the source document.  SERVER-6131
+
+t = db.jstests_aggregation_server6131;
+t.drop();
+
+function assertAggregationResults( expected, aggregation ) {
+    ret = t.aggregate( aggregation );
+    assert( ret.ok );
+    assert.eq( expected, ret.result );
+}
+
+t.drop();
+
+// An empty array document is dropped.
+t.save( { _id:0, a:1, b:[], c:2 } );
+assertAggregationResults( [], { $unwind:'$b' } );
+
+// Values from a nonempty array in another document are unwound.
+t.save( { _id:1, b:[ 4, 5 ] } );
+assertAggregationResults( [ { _id:1, b:4 },
+                            { _id:1, b:5 } ],
+                         { $unwind:'$b' } );
+
+// Another empty array document is dropped.
+t.save( { _id:2, b:[] } );
+assertAggregationResults( [ { _id:1, b:4 },
+                            { _id:1, b:5 } ],
+                         { $unwind:'$b' } );
+
+t.drop();
+
+// A nested empty array document is dropped.
+t.save( { _id:0, a:1, b:{ x:10, y:[], z:20 }, c:2 } );
+assertAggregationResults( [], { $unwind:'$b.y' } );
+
+t.drop();
+
+// A null value document is dropped.
+t.save( { _id:0, a:1, b:null, c:2 } );
+assertAggregationResults( [], { $unwind:'$b' } );
+
+t.drop();
+
+// A missing value causes the document to be dropped.
+t.save( { _id:0, a:1, c:2 } );
+assertAggregationResults( [], { $unwind:'$b' } );
+
+t.drop();
+
+// A missing value in an existing nested object causes the document to be dropped.
+t.save( { _id:0, a:1, b:{ d:4 }, c:2 } );
+assertAggregationResults( [], { $unwind:'$b.y' } );
+
+t.drop();
+
+// A missing value in a missing nested object causes the document to be dropped.
+t.save( { _id:0, a:1, b:10, c:2 } );
+assertAggregationResults( [], { $unwind:'$b.y' } );