PathMap class handles mapIndex field incorrectly.

mapIndex field in PathMap class keeps an Integer instance which represents
the path map index. But some methods treat it as int value incorrectly.

• equals(Object) compares mapIndex values using == operator.
  Naturally mapIndex values need to be compared using equals(Object).
• hashCode() dereferences mapIndex field without null check.
  So it causes NPE if mapIndex is null.

This issue was detected by FindBugs.