goja-core/src/main/java/goja/core/kits/reflect/ClassKit.java
public static String getPackageName(Class<?> clazz) {
        Preconditions.checkNotNull(clazz, "Class must not be null");
        return getPackageName(clazz.getName());
    }
public static String getPackageName(Class<?> clazz) {
        Preconditions.checkNotNull(clazz, "Class must not be null");
        return getPackageName(clazz.getName());
    }
Determine the name of the package of the given class,
e.g. "java.lang" for the {@code java.lang.String} class.

@param clazz the class
@return the package name, or the empty String if the class
is defined in the default package