Primary Language not returned with scan results for poi-ooxml-3.7.jar

A recent scan of poi-ooxml-3.7.jar at
http://central.maven.org/maven2/org/apache/poi/poi-ooxml/3.7/poi-ooxml-3.7.jar
returned useful results, but surprisingly did not return a Primary Language, which is obviously Java based on a quick visual inspection of the jar contents. Even though a `.class` file name extension may not be sufficient to identify the language as Java, there ought to be other clues in the binary jar to make it clear that the language is Java.

Scan results attached.
[poi-ooxml-3.7.jar_scan.json.zip](https://github.com/nexB/scancode-toolkit/files/2728008/poi-ooxml-3.7.jar_scan.json.zip)