web/play-java-forms/src/main/java/play/data/DynamicForm.java
public String get(String key) {
    try {
      return (String) get().getData().get(asNormalKey(key));
    } catch (Exception e) {
      return null;
    }
  }
public String get(String key) {
    try {
      return (String) get().getData().get(asNormalKey(key));
    } catch (Exception e) {
      return null;
    }
  }
Gets the concrete value only if the submission was a success. If the form is invalid because of
validation errors or you try to access a file field this method will return null. If you want
to retrieve the value even when the form is invalid use {@link #value(String)} instead. If you
want to retrieve a file field use {@link #file(String)} instead.

@param key the string key.
@return the value, or null if there is no match.