I am working with both the attiny and esp8266 chips. The idea is that with 1.6.4 I can add their boards manager package URL's in the preferences, open up the boards manager and simultaneously install whichever platforms I care to work with.
The reality is that both urls work separately but when I include them both and open up the manager I get a Java.lang.nullpointerException and can install neither. Furthermore if I close the IDE it fails to restart and I have to fix preferences.txt and clean up packages manually.
I have read the forums which suggest that you have to re-select your board. I tried this several times in various ways with no luck.
Relevant line from preferences.txt:
Strange line that does not seem to harm anything from preferences.txt: browser=mozilla,http://arduino.esp8266.com/package_esp8266com_index.json
Full error follows:
java.lang.NullPointerException java.lang.RuntimeException: java.lang.NullPointerException at cc.arduino.contributions.packages.ui.ContributionManagerUI$3.run(ContributionManagerUI.java:155) at java.lang.Thread.run(Thread.java:745) Caused by: java.lang.NullPointerException at cc.arduino.contributions.packages.ContributedToolReference.resolve(ContributedToolReference.java:43) at cc.arduino.contributions.packages.ContributedPlatform.resolveToolsDependencies(ContributedPlatform.java:76) at cc.arduino.contributions.packages.ContributionsIndexer.parseIndex(ContributionsIndexer.java:92) at processing.app.BaseNoGui.initPackages(BaseNoGui.java:600) at processing.app.Base$10.onIndexesUpdated(Base.java:1279) at cc.arduino.contributions.packages.ui.ContributionManagerUI$3.run(ContributionManagerUI.java:153) ... 1 more