code: func NewCompositeAggregation() *CompositeAggregation {
  	return &CompositeAggregation{
  		sources:         make([]CompositeAggregationValuesSource, 0),
  		subAggregations: make(map[string]Aggregation),
  	}
  }
docs: // NewCompositeAggregation creates a new CompositeAggregation.