StanfordParser may fail with NPE

[reckart]

Some problem here:

Caused by: java.lang.NullPointerException
    at de.tudarmstadt.ukp.dkpro.core.stanfordnlp.util.TreeWithTokens.setTree(TreeWithTokens.java:54)
    at de.tudarmstadt.ukp.dkpro.core.stanfordnlp.util.TreeWithTokens.<init>(TreeWithTokens.java:48)
    at de.tudarmstadt.ukp.dkpro.core.stanfordnlp.StanfordParser.process(StanfordParser.java:407)
    at org.apache.uima.analysis_component.JCasAnnotator_ImplBase.process(JCasAnnotator_ImplBase.java:48)
    at org.apache.uima.analysis_engine.impl.PrimitiveAnalysisEngine_impl.callAnalysisComponentProcess(PrimitiveAnalysisEngine_impl.java:385)
    ... 13 more

Apparently the tree object returned by the parser can be null:

de.tudarmstadt.ukp.dkpro.core.stanfordnlp.StanfordParser

                parseTree = query.getBestParse();
...
                sfAnnotator = new StanfordAnnotator(new TreeWithTokens(parseTree, tokens));

de.tudarmstadt.ukp.dkpro.core.stanfordnlp.util.TreeWithTokens

    public void setTree(Tree tree)
    {
        if (!(tree.label() instanceof CoreLabel)) {
            tree = tree.deepCopy(tree.treeFactory(), CoreLabel.factory());
        }