Sometimes users don't seem to notice/understand the <uniqueKey/> declaration in the example schema, and the error message they get if their documents don't include that field is confusing...
org.apache.solr.common.SolrException: Document [null] missing required field: id
...because they get an almost identical error even if they remove required=true from <field name="id" /> in their schema.xml file.
We should improve the error message so it's clear when a Document is missing the "uniqueKeyField" (not just a "required" field) so they know the terminology to look for in diagnosing the problem.
- is related to
SOLR-1780 existence of exactly one value for uniqueKey field is not checked when overwrite=false or allowDups=true