[PDFBOX-4906] PDOptionalContentProperties hasGroup can null pointer if OCGs data is missing

• Type: Bug
• Status: Closed
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: 2.0.13, 2.0.20
• Fix Version/s: 2.0.21, 3.0.0 PDFBox
• Assignee: Tilman Hausherr
• Reporter: Ryan Rupp
• Created: 30/Jun/20 20:17
• Updated: 21/Aug/20 04:54
• Resolved: 01/Jul/20 19:26

Description

I've noticed the following null pointer exception can happen on scanned documents when we're checking if it has a layer of a given name:

java.lang.NullPointerExceptionjava.lang.NullPointerException at org.apache.pdfbox.pdmodel.graphics.optionalcontent.PDOptionalContentProperties.getGroupNames(PDOptionalContentProperties.java:227) at org.apache.pdfbox.pdmodel.graphics.optionalcontent.PDOptionalContentProperties.hasGroup(PDOptionalContentProperties.java:245)

Looking into this, it happens because for these particular documents the following line returns null - https://github.com/apache/pdfbox/blob/da378798e5f2c8a1394725518db478f7ffaf5177/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/graphics/optionalcontent/PDOptionalContentProperties.java#L227

and subsequently gets dereferenced

It may be that these files are just generated in an invalid way (unfortunately I cannot provide them as it contains customer information). Anyway, looking at the code other methods getGroup(name) call a private method getOCGs that safeguards against the null case by defaulting it then, see here - https://github.com/apache/pdfbox/blob/da378798e5f2c8a1394725518db478f7ffaf5177/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/graphics/optionalcontent/PDOptionalContentProperties.java#L118

So maybe getGroupNames() (which hasGroup uses) can just use that as a safeguard? Anyway, the workaround was to replace our hasGroup(name) check with getGroup(name) != null