My module fails to display on administration page

thx but ive discovered the problem is not with the extension class tag in the the config.xmlfile… but its with the
“org.openmrs.module.web.extension.AdministrationSectionExt” which we must extend to. it seems the class sourcecode doesnt exist in the project. this iswat it says wen i hover over it

org.openmrs.module.web.extension.AdministrationSectionExt

Note: This element has no attached Javadoc and the Javadoc could not be found in the attached source.

and now this is the error in the log

java.lang.NoClassDefFoundError: org/openmrs/module/web/extension/AdministrationSectionExt
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
	at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
	at org.openmrs.module.ModuleClassLoader.loadClass(ModuleClassLoader.java:645)
	at org.openmrs.module.ModuleClassLoader.loadClass(ModuleClassLoader.java:564)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	at org.openmrs.module.Module.expandExtensionNames(Module.java:567)
	at org.openmrs.module.Module.getExtensions(Module.java:494)
	at org.openmrs.module.ModuleFactory.startModuleInternal(ModuleFactory.java:704)
	at org.openmrs.api.context.Daemon$1.run(Daemon.java:74)
Caused by: java.lang.ClassNotFoundException: org.openmrs.module.web.extension.AdministrationSectionExt
	at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1713)
	at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1558)
	at org.openmrs.module.ModuleClassLoader.loadClass(ModuleClassLoader.java:571)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)