ReadValue IllegalArgumentException: argument "content" is null

通过objectMapper.readValue();执行报错，异常信息如下

Exception in thread "main" java.lang.IllegalArgumentException: argument "content" is null
	at com.fasterxml.jackson.databind.ObjectMapper._assertNotNull(ObjectMapper.java:4737)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3435)

原因是因为调用readValue(参数, class)方法时，参数传了一个null导致