GH-4248 check for invalid triple context value

[abrokenjester]

GitHub issue resolved: #4248

Briefly describe the changes proposed in this PR:

• added explicit check in SailSourceConnection to avoid adding Triple as a context value
• added test coverage

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• my pull request is self-contained
• I've added tests for the changes I made
• I've applied code formatting (you can use mvn process-resources to format from the command line)
• I've squashed my commits where necessary
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