TextLogisticRegressionQParserPlugin, IGainTermsQParserPlugin and SignificantTermsQParserPlugin are similarly affected:
finish() contains this line of code:
Instead I think it should be this:
MultiFields can take some time to build and Solr (via SlowAtomicReader) has already done this work.
In addition, the code assumes Terms is non-null when in fact it will be null if there's no data.