NPE when <scm> section exists but has neither <connection> nor <developerConnection>

[jacobharris919]

The Spring Boot parent pom apparently adds an <scm> section to the POM. Effective POM contains:
<scm> <url>https://github.com/spring-projects/spring-boot/spring-boot-starter-parent/${project.name}</url> </scm>

Attempting to run 'mvn clean' with the gitflow-helper plugin activated yields the following error:

[ERROR] Internal error: java.lang.NullPointerException: The scm url cannot be null. -> [Help 1]
org.apache.maven.InternalErrorException: Internal error: java.lang.NullPointerException: The scm url cannot be null.
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:121)
        at org.apache.maven.cli.MavenCli.execute(MavenCli.java:863)
        at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:288)
        at org.apache.maven.cli.MavenCli.main(MavenCli.java:199)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
        at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: java.lang.NullPointerException: The scm url cannot be null.
        at org.apache.maven.scm.manager.AbstractScmManager.makeScmRepository(AbstractScmManager.java:195)
        at com.e_gineering.maven.gitflowhelper.ScmUtils.resolveBranchOrExpression(ScmUtils.java:60)
        at com.e_gineering.maven.gitflowhelper.MasterPromoteExtension.afterProjectsRead(MasterPromoteExtension.java:129)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:266)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:193)
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:106)
        ... 11 more