Object yamlObject = yaml.load(someYamlDocumentAsString);
// I only want to proceed if this YAML object is a Map<String, Object>
if ((yamlObject instanceof Map<?, ?>)) {
  Map<?, ?> propertyMap = (Map<?, ?>) yamlObject;
  for (Entry<?, ?> propertyEntry : propertyMap.entrySet()) {
    // I am checking each key and throwing if it's not a "String"
    Object propertyKey = propertyEntry.getKey();
    if (!(propertyKey instanceof CharSequence)) {
      throw new BananaException("FIXME"); // FIXME
    }
  }
} else {
  throw new CoconutException("FIXME"); // FIXME
}

@SuppressWarnings("unchecked")
Map<String, Object> aBeautifulAndCozyMap = (Map<String, Object>) propertyMap;