#fixed code
                                public FieldInfo propertyField(String propertyName) {
        if (propertyFields == null) {
            initPropertyFields();
        }
        return propertyFields.get(propertyName.toLowerCase());
    }
#vulnerable code 
                                public FieldInfo propertyField(String propertyName) {
        if (propertyFields == null) {

            if (propertyFields == null) {
                Collection<FieldInfo> fieldInfos = propertyFields();
                propertyFields = new HashMap<>(fieldInfos.size());
                for (FieldInfo fieldInfo : fieldInfos) {

                    propertyFields.put(fieldInfo.property().toLowerCase(), fieldInfo);
                }
            }
        }
        return propertyFields.get(propertyName.toLowerCase());
    } 
                            #location 9 
                            #vulnerability type NULL_DEREFERENCE