Files.probeContentType(Path) does return NULL for any file

Question

When determining the content type of a file with Files.probeFileContent(Path) for each file the result is null.

Environment:

java version "1.8.0"
Java(TM) SE Runtime Environment (build pap6480sr1fp1-20150603_01(SR1 FP1))
IBM J9 VM (build 2.8, JRE 1.8.0 AIX ppc64-64 Compressed References 20150410_243669 (JIT enabled, AOT enabled)
J9VM - R28_Java8_SR1_20150410_1531_B243669
JIT  - tr.r14.java_20150402_88976.03
GC   - R28_Java8_SR1_20150410_1531_B243669_CMPRSS
J9CL - 20150410_243669)
JCL - 20150601_01 based on Oracle jdk8u45-b13