Log tracer runs into ClassCastException for oak-queries

Oak's QueryEngineImpl logs the following "cost: {} for query {}" with the first parameter being a primitive double and the second being an instance of QueryImpl [1]. On the other hand the TraceContext casts thats second parameter to String without a type check [2]. I would propose to use String.valueOf() here to get the proper toString() implementation of the QueryImpl object.
 

[1] https://github.com/apache/jackrabbit-oak/blob/jackrabbit-oak-1.6.7/oak-core/src/main/java/org/apache/jackrabbit/oak/query/QueryEngineImpl.java#L311
[2] https://github.com/apache/sling-org-apache-sling-tracer/blob/master/src/main/java/org/apache/sling/tracer/internal/TracerContext.java#L92