solr4.7: truncated log output in grouping.CommandHandler?

[Jeff Wu <wu...@gmail.com>]

We had solr server 4.7 recently reported such WARN message, and come with a
long GC pause after that. Sometime it will force Solr server disconnect
with ZK server.

Solr 4.7.0, got this warning message:
WARN  - 2015-10-19 02:23:24.503;
org.apache.solr.search.grouping.CommandHandler; Query: +(+owner:testUser)
+(+directoryUUID:xxxxxxxxxxxxxxxxx +softFlag:`^H^@^@^@^@); Elapsed time:
20Exceeded allowed search time: 1 ms.

Questions is
The log string has sometring like this: `^H^@^@^@^@), this looks like a
truncated string. Is this expected output? Or indicating something wrong in
this query?