Getting key frames expression value independent of each other to another property

Hi,

I was wondering if anyone can let me know how to only get the key frame date from one layers effect property to another where it also has an Expressions applied to it, but if there are no key frames present it will revert to using the value from the expression.
I have tried using the - nearestKey(time) – however that only works if there is at least one key frame present.
So is there a way to write an expression that will look to the layers property to check if there is any key frames and if so use them exclusively (such as what happens if using nearestKey(time)) or if no key frames use the expression value.
Hope that does not sound too convoluted.

Kind Regards,

Tim