I have a year field on a content type, and I'm trying to enable a slider facet for that field.

When I do so, I get the "Search temporarily unavailble" message on the search page, and the following log entry:

HTTP Status 400 - Stats can only facet on single-valued fields, not: is_field_year[long{class=org.apache.solr.schema.TrieLongField,analyzer=org.apache.solr.analysis.TokenizerChain,args={precisionStep=0, positionIncrementGap=0, omitNorms=true}}]

The field is defined as Field Type List (integer) not just Field Type Integer - seems like that is the issue, even though it is set to only allow 1 value.

Is there some way to tell Apache Solr (using Acquia search) to treat this as a single-valued field?