picard ./gradlew test error

I have an error when tried to run ./gradle tests on my system.
I am running Linux Mint 18 system. Could you please let me know what should I do?
Thank you.

$ java -version
openjdk version "1.8.0_151"
OpenJDK Runtime Environment (build 1.8.0_151-8u151-b12-0ubuntu0.16.04.2-b12)
OpenJDK Server VM (build 25.151-b12, mixed mode)

$ git --version
git version 2.7.4

$ ll
total 108
drwxrwxr-x 10 usser usser 4096 Feb 20 21:50 ./
drwxr-xr-x 23 usser usser 4096 Feb 20 21:56 ../
drwxrwxr-x 3 usser usser 4096 Feb 20 21:51 build/
-rw-rw-r-- 1 usser usser 12763 Feb 20 20:52 build.gradle
-rw-rw-r-- 1 usser usser 1098 Feb 20 20:52 build.xml
-rw-rw-r-- 1 usser usser 358 Feb 20 20:52 .classpath
-rw-rw-r-- 1 usser usser 869 Feb 20 20:52 Dockerfile
-rw-rw-r-- 1 usser usser 179 Feb 20 20:52 .dockerignore
drwxrwxr-x 3 usser usser 4096 Feb 20 20:52 etc/
drwxrwxr-x 8 usser usser 4096 Feb 20 20:52 .git/
drwxrwxr-x 2 usser usser 4096 Feb 20 20:52 .github/
-rw-rw-r-- 1 usser usser 190 Feb 20 20:52 .gitignore
drwxrwxr-x 3 usser usser 4096 Feb 20 20:52 gradle/
-rwxrwxr-x 1 usser usser 5046 Feb 20 20:52 gradlew*
-rw-rw-r-- 1 usser usser 1072 Feb 20 20:52 LICENSE.txt
drwxrwxr-x 2 usser usser 4096 Feb 20 20:52 project/
-rw-rw-r-- 1 usser usser 356 Feb 20 20:52 .project
-rw-rw-r-- 1 usser usser 6045 Feb 20 20:52 README.md
-rw-rw-r-- 1 usser usser 56 Feb 20 20:52 settings.gradle
drwxrwxr-x 4 usser usser 4096 Feb 20 20:52 src/
drwxrwxr-x 3 usser usser 4096 Feb 20 20:52 testdata/
-rw-rw-r-- 1 usser usser 601 Feb 20 20:52 .travis.yml

$ ./gradlew test

FAILURE: Build failed with an exception.

• Where:
  Build file '/home/usser/picard/build.gradle' line: 55

• What went wrong:
  A problem occurred evaluating root project 'picard'.

  Cannot invoke method getURLs() on null object

• Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED

Total time: 1.695 secs