I'm having the same issue trying to debug GPIO_IOToggle example for the Nucleo-F401.

> An internal error occurred during: "Launching STM32F4xx-Nucleo Debug".
> java.lang.NullPointerException

Any help would be appreciated.

BTW, my Java version is 1.7.0_79

And here's my logs:

SESSION 2015-10-06 11:53:01.065 -------------------

eclipse.buildId=4.4.2.M20150204-1700
java.version=1.7.0_79
java.vendor=Oracle Corporation
BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=en_US
Framework arguments: -product org.eclipse.epp.package.cpp.product
Command-line arguments: -os win32 -ws win32 -arch x86_64 -product org.eclipse.epp.package.cpp.product

....

ENTRY org.eclipse.core.jobs 4 2 2015-10-06 17:17:50.175

MESSAGE An internal error occurred during: "Launching STM32F4xx-Nucleo Debug".

STACK 0

java.lang.NullPointerException
at fr.ac6.mcu.debug.launching.MCUGdbLaunch.createOpenOCDProgramProcess(MCUGdbLaunch.java:141)
at fr.ac6.mcu.debug.launching.MCUGdbLaunch.addOpenOCDProcess(MCUGdbLaunch.java:67)
at fr.ac6.mcu.debug.launching.MCUGDBJtagDSFLaunchConfigurationDelegate.launch(MCUGDBJtagDSFLaunchConfigurationDelegate.java:98)
at org.eclipse.debug.internal.core.LaunchConfiguration.launch(LaunchConfiguration.java:885)
at org.eclipse.debug.internal.core.LaunchConfiguration.launch(LaunchConfiguration.java:739)
at org.eclipse.debug.internal.ui.DebugUIPlugin.buildAndLaunch(DebugUIPlugin.java:1039)
at org.eclipse.debug.internal.ui.DebugUIPlugin$8.run(DebugUIPlugin.java:1256)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)