I came here after finding this problem.

In my specific case it turned out that I downloaded the download page from the apache server and not the model itself.

The property problem probably means that the SentenceModel couldn't unzip your model file and read it as a resource.

java.lang.NullPointerException: Cannot invoke "java.util.Properties.getProperty(String)" because "manifest" is null

    at opennlp.tools.util.model.BaseModel.getManifestProperty(BaseModel.java:542)
    at opennlp.tools.util.model.BaseModel.initializeFactory(BaseModel.java:281)
    at opennlp.tools.util.model.BaseModel.loadModel(BaseModel.java:266)
    at opennlp.tools.util.model.BaseModel.<init>(BaseModel.java:173)
    at opennlp.tools.sentdetect.SentenceModel.<init>(SentenceModel.java:69)