code: public boolean containsKey(Object propertyName) {
          if (propertyName instanceof CharSequence) propertyName = propertyName.toString();
          Assert.isInstanceOf(String.class, propertyName, "This map implementation only supports String based keys!");
  
          String pn = propertyName.toString();
          return !NameUtils.isConfigurational(pn) && metaClass.getMetaProperty(pn) != null;
      }
docs: {@inheritDoc}
  @see java.util.Map#containsKey(java.lang.Object)