@Override
	public ExpertEntity getExpertById(Long id) {
		ExpertEntity Expert = ExpertMapper.getObjectById(id);
		if (Expert.getFilepath().length()>1) {
			...
		}
		return Expert;
	}

对象的Stirng的length大于1就进行操作，很理想对不对，然而报空指针错误

解决方案：

@Override
	public ExpertEntity getExpertById(Long id) {
		ExpertEntity Expert = ExpertMapper.getObjectById(id);
		if (Expert.getFilepath()!=null && Expert.getFilepath().length()>1) {
			...
		}
		return Expert;
	}