Test diag:
@startuml
class test
newpage
class test2
@enduml
Two latest versions 1.2018.4 and 1.2018.5 crash with following output from console:
Exception in thread "main" java.lang.NullPointerException
at net.sourceforge.plantuml.SourceFileReaderAbstract.getGeneratedImages(SourceFileReaderAbstract.java:162)
at net.sourceforge.plantuml.Run.manageFileInternal(Run.java:422)
at net.sourceforge.plantuml.Run.processArgs(Run.java:333)
at net.sourceforge.plantuml.Run.manageAllFiles(Run.java:303)
at net.sourceforge.plantuml.Run.main(Run.java:163)
The cause is the newpage expression. WIthout it works fine.
Older versions, for example 1.2018.3 don't have this issue.