Same problem. Mac Os X 10.10.2. Spark Version 2.6.3 (12555)
$ java -version
java version "1.8.0_40"
Java(TM) SE Runtime Environment (build 1.8.0_40-b27)
Java HotSpot(TM) 64-Bit Server VM (build 25.40-b25, mixed mode)
$ /usr/libexec/java_home
/Library/Java/JavaVirtualMachines/jdk1.8.0_40.jdk/Contents/Home
/usr/bin/java -> /Library/Internet Plug-Ins/JavaAppletPlugin.plugin/Contents/Home/bin/java