Ensure params are applied independently

[ninoslavmilenovic]

Fixes

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

Allows for optional params for the Mail object to be applied even if not all of them are supplied.

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[SendGridDX]

All committers have signed the CLA.

[thinkingserious]

Thanks @rubyengineer! This in on our backlog for code review.

[thinkingserious]

Hello @rubyengineer,

Thanks again for the PR!

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