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// SERVER-14691: $avg aggregator should return null when it receives no input.
(function() {
'use strict';
var coll = db.accumulate_avg_sum_null;
// Test the $avg aggregator.
coll.drop();
// Null cases.
assert.writeOK(coll.insert({a: 1, b: 2, c: 'string', d: null}));
// Missing field.
var pipeline = [{$group: {_id: '$a', avg: {$avg: '$missing'}}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{_id: 1, avg: null}]);
// Non-numeric field.
pipeline = [{$group: {_id: '$a', avg: {$avg: '$c'}}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{_id: 1, avg: null}]);
// Field with value of null.
pipeline = [{$group: {_id: '$a', avg: {$avg: '$d'}}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{_id: 1, avg: null}]);
// All three.
coll.insert({a: 1, d: 'string'});
coll.insert({a: 1});
pipeline = [{$group: {_id: '$a', avg: {$avg: '$d'}}}];
assert.eq(coll.aggregate(pipeline).toArray(), [{_id: 1, avg: null}]);
// Non-null cases.
coll.drop();
assert.writeOK(coll.insert({a: 1, b: 2}));
pipeline = [{$group: {_id: '$a', avg: {$avg: '$b'}}}];
// One field.
assert.eq(coll.aggregate(pipeline).toArray(), [{_id: 1, avg: 2}]);
// Two fields.
assert.writeOK(coll.insert({a: 1, b: 4}));
assert.eq(coll.aggregate(pipeline).toArray(), [{_id: 1, avg: 3}]);
// Average of zero should still work.
assert.writeOK(coll.insert({a: 1, b: -6}));
assert.eq(coll.aggregate(pipeline).toArray(), [{_id: 1, avg: 0}]);
// Missing, null, or non-numeric fields should not error or affect the average.
assert.writeOK(coll.insert({a: 1}));
assert.writeOK(coll.insert({a: 1, b: 'string'}));
assert.writeOK(coll.insert({a: 1, b: null}));
assert.eq(coll.aggregate(pipeline).toArray(), [{_id: 1, avg: 0}]);
}());
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