[MRELEASE-872] NPE in release:perform when specifying svn tag as param

**[Anders Hammar](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=afloom)** opened **[MRELEASE-872](https://issues.apache.org/jira/browse/MRELEASE-872?redirect=false)** and commented

When executing release:perform and specifying the Svn tag via the 'connectionUrl' parameter, the execution fails with a NullPointerException. This happens for an execution without an existing Maven project (e.g. in an empty directory).

> [ERROR] Failed to execute goal org.apache.maven.plugins:maven-release-plugin:2.5:perform (default-cli) on project standalone-pom: Execution default-cli of goal org.apache.maven.plugins:maven-release-plugin:2.5:perform failed. NullPointerException -> [Help 1]
> org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-release-plugin:2.5:perform (default-cli) on project standalone-pom: Execution default-cli
> of goal org.apache.maven.plugins:maven-release-plugin:2.5:perform failed.
> at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:225)
> 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:320)
> 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:60)
> at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
> at java.lang.reflect.Method.invoke(Method.java:611)
> 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.PluginExecutionException: Execution default-cli of goal org.apache.maven.plugins:maven-release-plugin:2.5:perform failed.
> at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:110)
> at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:209)
> ... 19 more
> Caused by: java.lang.NullPointerException
> at org.apache.maven.shared.release.util.ReleaseUtil.getCommonBasedir(ReleaseUtil.java:210)
> at org.apache.maven.shared.release.util.ReleaseUtil.getCommonBasedir(ReleaseUtil.java:200)
> at org.apache.maven.shared.release.phase.CheckoutProjectFromScm.performCheckout(CheckoutProjectFromScm.java:230)
> at org.apache.maven.shared.release.phase.CheckoutProjectFromScm.execute(CheckoutProjectFromScm.java:131)
> at org.apache.maven.shared.release.DefaultReleaseManager.perform(DefaultReleaseManager.java:429)
> at org.apache.maven.shared.release.DefaultReleaseManager.perform(DefaultReleaseManager.java:381)
> at org.apache.maven.plugins.release.PerformReleaseMojo.execute(PerformReleaseMojo.java:177)
> at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:101)
> ... 20 more

---

**Affects:** 2.4.2, 2.5

Reproduce release:perform from an empty directory with connectionUrl set to an SVN tag. Start with ReleaseUtil.getCommonBasedir and CheckoutProjectFromScm.performCheckout, the locations shown in the stack trace. Done means this scenario no longer fails with a NullPointerException and has an appropriate release:perform result.

Written by the indexing model from the issue text.