code: public final boolean isRemoved(final String key) {
          final Property prop = find(key);
          if (prop == null) {
              return true;
          }
          return prop.isDeleted();
      }
docs: Returns if a property has been deleted.
  
  @param key
  Key for the property to check.
  
  @return If the property is unknown or has been deleted <code>true</code> else <code>false</code>.