加载依赖性解析器期间的Nullpointer异常

Question

我正在使用stanford-corenlp-3.5.2和德语解析模型germanFactored.ser.gz。代码工作正常，直到我尝试进行依赖解析。在初始化SemanticGraph时，我会检索NullPointerException。

加载：CollapsedCCProcessedDependenciesAnnotation.class（第一行抛出异常）

SemanticGraph dependencies = sentence.get(CollapsedCCProcessedDependenciesAnnotation.class);
System.out.println(dependencies);    
dependencies.prettyPrint();

整个代码：

public static void main(String[] args) {
    Properties props = new Properties();
    props.put("annotators", "tokenize, ssplit, pos, lemma, ner, parse");
    props.put("parse.model", "edu/stanford/nlp/models/lexparser/germanFactored.ser.gz");
    props.put("ner.model", "edu/stanford/nlp/models/ner/german.dewac_175m_600.crf.ser.gz");
    props.put("pos.model", "edu/stanford/nlp/models/pos-tagger/german/german-hgc.tagger");
    props.put("parse.flags", "");

    StanfordCoreNLP pipeline = new StanfordCoreNLP(props);
    String text = "Sehr gute Kenntnisse in Englisch und Deutsch sowie Programmierkenntnisse (C#, Java, C++).";                                                                                                                                              // text
    Annotation document = new Annotation(text);
    pipeline.annotate(document);

    List<CoreMap> sentences = document.get(SentencesAnnotation.class);

    for (CoreMap sentence : sentences) {
        for (CoreLabel token : sentence.get(TokensAnnotation.class)) {
            String word = token.get(TextAnnotation.class);
            String pos = token.get(PartOfSpeechAnnotation.class);
            String ne = token.get(NamedEntityTagAnnotation.class);

            System.out.println(String.format("%s - %s - %s", word, pos, ne));
        }

        Tree tree = sentence.get(TreeAnnotation.class);
        System.out.println(tree.toString());

        try {
            SemanticGraph dependencies = sentence.get(CollapsedCCProcessedDependenciesAnnotation.class);
            System.out.println(dependencies);

            dependencies.prettyPrint();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}