fix(Utils): add guard against null rule value in validateRule

[afsuyadi]

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Changes

Contributes to #7536

1. Error happens when CreateSegment component is trying to call method validateRule() by passing an object.
2. The method crashes when split() method is executed on a variable that isn't string-type.
3. Inside method validateRule(), only value prop that is accessed and doesn't have its own guard, so the method crashes when it's empty (either null or undefined).
4. I add loose equality guard, to catch only null and undefined value.

How did you test this code?

1. I try to simulate this on my local by manually creating the Segment via UI, but it seems no error happens, because the button Create Segment itself is already been greyed out.
2. I deduce that this error happens via API backend hit.

Screencast.from.14-06-26.11.46.58.webm

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