FULL PRODUCT VERSION :
java 9-ea
Java(TM) SE Runtime Environment (build 9-ea+159)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+159, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Windows 10 Enterprise

A DESCRIPTION OF THE PROBLEM :
I call Class method (e.g. getDeclaredFields) from JNI -- no Java code on thread stack before Class.getDeclaredFields.

checkMemberAccess in this case always throws NPE:
java.lang.NullPointerException
at java.base/java.lang.Class.checkMemberAccess(Unknown Source)
at java.base/java.lang.Class.getDeclaredFields(Unknown Source)
        <My JNI code>

Problematic line of code (\java.base\java\lang\Class.java:2774) :
final ClassLoader ccl = caller.getClassLoader0();

caller is always null in my case.

Proposal:
final ClassLoader ccl = ClassLoader.getClassLoader(caller);


REGRESSION. Last worked in version 8u121


REPRODUCIBILITY :
This bug can be reproduced always.