web/play-java-forms/src/main/java/play/data/Form.java
public T get(Lang lang) {
    if (!errors.isEmpty()) {
      throw new IllegalStateException("Error(s) binding form: " + errorsAsJson(lang));
    }
    return value.get();
  }
public T get(Lang lang) {
    if (!errors.isEmpty()) {
      throw new IllegalStateException("Error(s) binding form: " + errorsAsJson(lang));
    }
    return value.get();
  }
Gets the concrete value only if the submission was a success. If the form is invalid because of
validation errors this method will throw an exception. If you want to retrieve the value even
when the form is invalid use {@link #value()} instead.

@param lang if an IllegalStateException gets thrown it's used to translate the form errors
within that exception
@throws IllegalStateException if there are errors binding the form, including the errors as
JSON in the message
@return the concrete value.