Trust anchor for certification path not found in Microsoft Graph API

Question

I have been using the Microsoft Graph API in my android application to get the calendar events etc... The Authentication and events data retrieval were all working fine, but Microsoft Graph is not working properly on devices under 4.4 lately, when I try to get user data or calendar events, an exception occurs. I run the same codes on 2 android SDK versions, on 6.0, I can get all the data I want but on 4.4, it fails with the exception:

Caused by: java.security.cert.CertificateException: java.security.cert.CertPathValidatorException: Trust anchor for certification path not found.

Please suggest solutions for resolving this issue.