Null exception in drawImage

Hello, I'm using your library with a premium license.
I need to create in Android some pdf with an image per page. I have tested and taken parts of code from your examples.
During the generation of the pdf, every so often, for no apparent reason, the function "drawImage (hand, image.hand);" goes to "null Exception".
In debug mode I can not replicate the error, and in running mode only after N insertions.
I think "page.AddResImage (dimg);" returns null, but I don't know why.
For us it is a big problem that does not allow us to go live.
Do you have suggestions?

Do you invoke: m_doc.SetCache( file_cache );//set temporary cache for editing.

You can also check www.androidpdf.mobi/forum/Android-develo...remely-slow?start=12

Yes:

String file_cache = Global.tmp_path + "/temp.dat";
m_doc = new Document();
m_doc.Create(file);
m_doc.SetCache(file_cache);
...