Use constant for empty string like as ""

Comment From: pivotal-cla

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Comment From: pivotal-cla

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Comment From: sbrannen

Hi @nastae,

Congratulations on submitting your first PR for the Spring Framework! 👍

Regarding the empty string, we have over 3700 occurrences within the code base, and we don't see the need to define that as a constant simply because it's such a common value and the use of a constant would not provide much value in terms of readability or maintenance.

In light of that, I am closing this PR.

Regards,

Sam