The egit [1] and egit-github [2] gerrit-trigger build jobs used to verify
 changes uploaded for code review experience some strange errors
 since a couple of days. 
 [1] reproducably hits a NPE (using tycho 0.12) 
 [ERROR] Failed to execute goal org.eclipse.tycho:tycho-p2-
plugin:0.12.0:update-site-p2-
metadata (default-update-site-p2-
metadata) on project org.eclipse.egit-updatesite: Cannot generate P2 metadata: java.lang.NullPointerException ->  [Help 1]
 org.apache.maven.lifecycle.
LifecycleExecutionException: Failed to execute goal org.eclipse.tycho:tycho-p2-
plugin:0.12.0:update-site-p2-
metadata (default-update-site-p2-
metadata) on project org.eclipse.egit-updatesite: Cannot generate P2 metadata
         at org.apache.maven.lifecycle.
internal.MojoExecutor.execute(
MojoExecutor.java:217)
        at org.apache.maven.lifecycle.
internal.MojoExecutor.execute(
MojoExecutor.java:153)
        at org.apache.maven.lifecycle.
internal.MojoExecutor.execute(
MojoExecutor.java:145)
        at org.apache.maven.lifecycle.
internal.
LifecycleModuleBuilder.
buildProject(
LifecycleModuleBuilder.java:
84)
        at org.apache.maven.lifecycle.
internal.
LifecycleModuleBuilder.
buildProject(
LifecycleModuleBuilder.java:
59)
        at org.apache.maven.lifecycle.
internal.LifecycleStarter.
singleThreadedBuild(
LifecycleStarter.java:183)
        at org.apache.maven.lifecycle.
internal.LifecycleStarter.
execute(LifecycleStarter.java:
161)
        at org.apache.maven.DefaultMaven.
doExecute(DefaultMaven.java:
319)
        at org.apache.maven.DefaultMaven.
execute(DefaultMaven.java:156)
        at org.apache.maven.cli.MavenCli.
execute(MavenCli.java:537)
        at org.apache.maven.cli.MavenCli.
doMain(MavenCli.java:196)
        at org.apache.maven.cli.MavenCli.
main(MavenCli.java:141)
        at sun.reflect.
NativeMethodAccessorImpl.
invoke0(Native Method)
        at sun.reflect.
NativeMethodAccessorImpl.
invoke(
NativeMethodAccessorImpl.java:
39)
        at sun.reflect.
DelegatingMethodAccessorImpl.
invoke(
DelegatingMethodAccessorImpl.
java:25)
        at java.lang.reflect.Method.
invoke(Method.java:597)
        at org.codehaus.plexus.
classworlds.launcher.Launcher.
launchEnhanced(Launcher.java:
290)
        at org.codehaus.plexus.
classworlds.launcher.Launcher.
launch(Launcher.java:230)
        at org.codehaus.plexus.
classworlds.launcher.Launcher.
mainWithExitCode(Launcher.
java:409)
        at org.codehaus.plexus.
classworlds.launcher.Launcher.
main(Launcher.java:352)
 Caused by: org.apache.maven.plugin.
MojoExecutionException: Cannot generate P2 metadata
        at org.eclipse.tycho.plugins.p2.
AbstractP2MetadataMojo.
execute(
AbstractP2MetadataMojo.java:
95)
        at org.apache.maven.plugin.
DefaultBuildPluginManager.
executeMojo(
DefaultBuildPluginManager.
java:101)
        at org.apache.maven.lifecycle.
internal.MojoExecutor.execute(
MojoExecutor.java:209)
        ... 19 more
 Caused by: java.lang.RuntimeException: java.lang.NullPointerException
        at org.eclipse.tycho.p2.facade.
internal.
P2ApplicationLauncher.execute(
P2ApplicationLauncher.java:
127)
        at org.eclipse.tycho.plugins.p2.
AbstractP2MetadataMojo.
generateMetadata(
AbstractP2MetadataMojo.java:
112)
        at org.eclipse.tycho.plugins.p2.
AbstractP2MetadataMojo.
execute(
AbstractP2MetadataMojo.java:
88)
        ... 21 more
 Caused by: java.lang.NullPointerException
        at org.eclipse.tycho.core.
osgitools.DefaultBundleReader.
toProperties(
DefaultBundleReader.java:162)
        at org.eclipse.tycho.core.
osgitools.DefaultBundleReader.
parseHeader(
DefaultBundleReader.java:173)
        at org.eclipse.tycho.core.
osgitools.OsgiBundleProject.
readArtifactKey(
OsgiBundleProject.java:130)
        at org.eclipse.tycho.p2.facade.
internal.
P2ApplicationLauncher.
addBundle(
P2ApplicationLauncher.java:
132)
        at org.eclipse.tycho.p2.facade.
internal.
P2ApplicationLauncher.execute(
P2ApplicationLauncher.java:99)
        ... 23 more  
 [2] (using tycho 0.13) seems to fail to download some of the tycho
 plugins and then fails with a ClassNotFoundException 
 Wiping the workspace to remove the job private maven repo doesn't seem
 to help in both cases.
 I tried this many times, also Jan Sievers looked into these failing jobs
 and we are running out
 of ideas what could be the cause of these.build errors. Today I also saw
 the second issue when
 running the egit-github build locally. Again wiping the local maven
 repository didn't resolve the
 issue. What helped was to remove the tycho plugins from the local maven
 repository and then
 rerunning the build, wiping the complete Maven repository didn't help. 
 [1] 
https://hudson.eclipse.org/sandbox/job/egit.gerrit/ [2] 
https://hudson.eclipse.org/sandbox/job/egit-github.gerrit/  --
 Matthias