title: IntelliJ IDEA underlines variables when using += in JAVA
body: <p>Since the new update (2018.2) IntelliJ IDEA underlines variables, when they are "unnecessarily" reassigned - this includes, however, each use of "+=".<br>
  Is this a mistake in the IDE or am I getting it wrong?<br>
  Please see this basic method as an example. (It just adds a list of numbers.)<br></p>
  
  <p><a href="https://i.stack.imgur.com/bxLKB.png" rel="noreferrer"><img src="https://i.stack.imgur.com/bxLKB.png" alt="example image"></a></p>