Final Field Initialization With Exceptions

consider:
 
class A {
     final Object b;
     public A(C c) {
          try {
               b = c.someMethodThatMayThrowSomeException();
          } catch (SomeException e) {
               b = null; // This line results in compiler error: "variable b might already have been assigned"
          }
     } // take away b=null line and you get "variable b might not have been initialized" on this line
}
 
Why? How could 'b' be assigned if the exception was thrown?
 
Btw, the workaround is to wrap the method call:
 
private final Object initB() {
     try {
          return c.someMethodThatMayThrowSomeException();
     } catch (SomeException e) {
          return null;
     }
}
 
and use b = initB(); in the constructor.  But that seems like it should be unnecessary.