code: public JsonModelCoder<T> fix() {
  		Map<String, JsonPropertyCoder<T, ?>> properties =
  				new LinkedHashMap<String, JsonPropertyCoder<T, ?>>();
  		for (String key : map.keySet()) {
  			JsonPropertyBuilder<T, ?> builder = map.get(key);
  			JsonPropertyCoder<T, ?> fixed = builder.fix();
  			properties.put(key, fixed);
  		}
  
  		JsonModelCoder<T> fixed =
  				new JsonModelCoder<T>(baseClass, treatUnknownKeyAsError, properties);
  		return fixed;
  	}
docs: Fixiates the current state for coding.
  @return A JsonModelCoder instance for the actual coding.
  @author vvakame