RHV: Exception while parsing JSON for disk

Issue

In /var/log/ovirt-engine/engine.log, several occurrences of the following WARNING are seen:

2017-08-21 13:41:45,435+10 WARN  [org.ovirt.engine.core.bll.storage.disk.image.GetUnregisteredDiskQuery] (org.ovirt.thread.pool-6-thread-48) [b56aacc1-c32e-49be-8c67-15897edb9783] Exception while parsing JSON for disk. Exception: '{}': org.codehaus.jackson.JsonParseException: Unexpected character ('g' (code 103)): expected a valid value (number, String, array, object, 'true', 'false' or 'null')
 at [Source: java.io.StringReader@3556c5d1; line: 1, column: 2]
        at org.codehaus.jackson.JsonParser._constructError(JsonParser.java:1433) [jackson-core-asl.jar:1.9.13.redhat-3]
        at org.codehaus.jackson.impl.JsonParserMinimalBase._reportError(JsonParserMinimalBase.java:521) [jackson-core-asl.jar:1.9.13.redhat-3]