NullPointerException when disabling a servlet plugin

Looks like PathMapper.put(path, null) doesn't do what we think it does.

java.lang.NullPointerException
at com.atlassian.seraph.util.PathMapper.put(PathMapper.java:59)
at com.atlassian.confluence.plugin.descriptor.servlet.ServletModuleManager.removeModule(ServletModuleManager.java:83)
at com.atlassian.confluence.plugin.descriptor.servlet.ServletModuleDescriptor.disabled(ServletModuleDescriptor.java:61)
at com.atlassian.plugin.DefaultPluginManager.disablePlugin(DefaultPluginManager.java:260)
at com.atlassian.confluence.plugin.ConfluencePluginManager.disablePlugin(ConfluencePluginManager.java:80)
at com.atlassian.confluence.admin.actions.plugins.ManagePluginsAction.execute(ManagePluginsAction.java:47)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:168)
at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:35)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.atlassian.confluence.security.actions.PermissionCheckInterceptor.intercept(PermissionCheckInterceptor.java:40)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.atlassian.confluence.pages.actions.PageAwareInterceptor.intercept(PageAwareInterceptor.java:94)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.atlassian.confluence.spaces.actions.SpaceAwareInterceptor.intercept(SpaceAwareInterceptor.java:82)