Is it possible to index a default value when a document property is undeclared?

Elastic Stack Elasticsearch
1

I'd like ElasticSearch to index a default value for a property when that
property is not defined when the document is created. At first I thought
null_value did this, but now I realize this only helps when the property is
defined as NULL.

Is it possible to index a default value when a document property is
undeclared?

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