[#3826] - Status Code 500 / NullPointerException in "Reports" when report moved

After cut/pasting a report from one folder to another using the Jasper Server admin console, calling the REST v2 "reports" command with the path to the old report will return Status Code 500, with the following XML:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?><errorDescriptor><errorCode>unexpected.error</errorCode><message>Unexpected error</message><parameters><parameter>java.lang.NullPointerException</parameter></parameters></errorDescriptor>

Should probably return 404 - Not Found status code in this case.

Steps to reproduce:
1. Create report in the Jasper Server repository in one folder.
2. Access that report using REST v2 (e.g. /jasperserver/rest_v2/reports/reports/abc/TestReport.pdf). The report is returned successfully as PDF.
3. Cut / Paste the report to another folder (e.g. to /reports/def)
4. Access report in old location using REST v2 (e.g. /jasperserver/rest_v2/reports/reports/abc/TestReport.pdf) using the same session.
5. Instead of 404, internal error 500 is returned with the above, and will continue to do so until another session is started.

Reason why this might be significant:
"500" is too general of an error. I'd like to handle 404 errors differently than 500 errors.