KNOX-2763 Fix for NPE arising due to missing CompositeAuthz provider names

[harshiljhaveri]

What changes were proposed in this pull request?

The Provider Names Parse Method handles the case where no provider names or blank or empty provider names are provided.

How was this patch tested?

Comprehensive unit tests written. Also manually tested

Knox Contributing Process reviewed.

[harshiljhaveri]

@moresandeep @smolnar82 @zeroflag

[smolnar82]

@harshiljhaveri - is this the same PR as #597?

[harshiljhaveri]

@harshiljhaveri - is this the same PR as #597?

Yes, PR 597 had conditions to handle null cases as well. Started a new PR to address a different JIRA ticket #.

[smolnar82]

Closing this because it's the same as #597