Solr Query - return all results that do not contain a certain field
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Is there any way to write a query that will return all results that do not contain a certain field? 

For example, let's say that I have an index of people that contains firstName, lastName and birthDate. I want to query for all people who do not have a birthDate. NOT all people where birthDate is null, but all people where there simply is no birthDate field. Is this possible?