in src/nms-api/Util/PrimitiveMap.cs [244:253]
public IDictionary GetDictionary(String key)
{
Object value = GetValue(key);
if (value != null && !(value is IDictionary))
{
throw new NMSException("Property: " + key + " is not an IDictionary but is: " + value);
}
return (IDictionary) value;
}