[UserStory] Create JUnit Test for Redistrctor.java IllegalArgumentException

[tdefo]

User Story
Essential components
Title describes the story
Stakeholder type is identified
Outcome is described
Rationale is explicit
Acceptance criteria are verifiable and from the perspective of the stakeholder
Story
As a Developer
I want a JUnit test that ensures an exception is thrown when null region is used in Redistrictor.
so that code is tested to verify values.

Acceptance Criteria
Write a test that anticipates an IllegalArgumentException when theRegion is null.

Scenario 1
Given A unit test Redistrictor verifying exception throw.
when the theRegion has a value of null
then receive IllegalArgumentException

##Reference
https://github.com/MetroCS/redistricting/blob/d022764cba3f008981a08c2cedc0b2771548a6d6/src/swdmt/redistricting/Redistrictor.java#L30-L42

Dependents
Issue #28

[tdefo]

Tested this error to make sure it works by changing the test of theRegion to check if it is not null and if it was not null, it would throw exception. Exception was thrown.