Micro flow bringing correct data but with null at start of list

Hi all,   i am having an issue with my microflow where it is starting the list with the word null. I am retrieving a list and changing an object in a loop to pull data from all records into a single report-like pop-up. Please see the microflow i am referring to below.    would anyone have any idea on how to get rid of the null.    
1 answers

The EvidenceDetails attribute is empty when it is first used, so when you add a String to it it is turning that into ‘null’. 

You may find it easier to create a String variable and initialise this with ‘’. You can then append your other Strings to this, and at the end of the microflow assign this variable to the EvidenceDetails attribute.

I hope this helps.