improve error message for XML where the spec attribute is missing #28

src/beast/pkgmgmt/BEASTClassLoader.java

@@ -149,6 +149,7 @@ public static Class<?> forName(String className, String service) throws ClassNot
 			if (!services.get(service).contains(className)) {
 				throw new ClassNotFoundException("Could not find class " + className + " as service " + service + "\n"
 						+ "Perhaps the package is missing or the package is not correctly configured by the developer "
+						+ (className.equals("beast.base.core.BEASTInterface") ? "\nor there is an element without spec attribute\n" : "") 
 						+ "(Developer: check by running beastfx.app.tools.PackageHealthChecker on the package)");
 			}
 			ClassLoader loader = class2loaderMap.get(className);