Stops on download error with an exception?

[Dither]

The application stops execution with:

[ERROR] filename.png 
java.io.FileNotFoundException: filename.png
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
...
    at net.nczonline.web.datauri.DataURIGenerator.generateDataURI(DataURIGen
erator.java:182)
...

Is it how it supposed to work without --skip-missing parameter? Also what do you think about changing behavior to skipping missing files by default and --break-on-error parameter which configures application to stop and display failing CSS-code in console on error?