Fix "DoubleCheckedLocking" race condition in initialization of the REST resources found by PMD.
In short, if a variable shared by multiple threads is assigned, and the expression on the right hand side is an object construction, then an optimizing JDK is allowed to assign the variable first and then call the constructor.
Be aware that the top Google results on this are from the JDK 1.4 times (and earlier), and suggest the "double-checked locking" is an anti-pattern. That was perhaps true back then. The proper fix since JDK 1.5 is to make the variables volatile.