Nullability handling improvements, including fixes #31

First two commits were required solely to set up my workflow and make IDE shut up, so feel free to revert them, if you want.

Also includes fix to bug with restoring Character/Byte variables (the existence of bug itself being another proof that _nobody_ uses those nowdays).
Please wrap your if statements with curly braces.
Do so for the generated classes as well, like so
```java
    result = ... concatenation without StringBuilder... 
    if (field.isNullable()) {
       result = "if .... {" + result + "\n}";
   }
   return result;
```