#vulnerable code 
                                @Override
    public String unique(final CacheMeta meta) {
        final Class<?> entityCls = meta.type();
        final TreeMap<String, String> treeMap = new TreeMap<>();
        treeMap.put(meta.primaryString(), this.id);
        return CacheTool.keyId(entityCls.getName(), treeMap);
    } 
                            #location 6 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public String unique(final CacheMeta meta) {
        final TreeMap<String, String> treeMap = new TreeMap<>();
        treeMap.put(meta.primaryString(), this.id);
        return CacheTool.keyId(meta.typeName(), treeMap);
    }