又一则报错

FindBugs: May expose internal representation by returning reference to mutable object Returning a reference to a mutable object value stored in one of the object's fields exposes the internal representation of the object. If instances are accessed by untrusted code, and unchecked changes to the mutable object would compromise security or other important properties, you will need to do something different. Returning a new copy of the object is better approach in many situations.

try to define a inconstant return value for the function.