magento 2 - Error filtering template: Notice: Trying to access array offset on value of type null

[Aveeva]

I am getting

Error filtering template: Notice: Trying to access array offset on value of type null in C:\xampp\htdocs\m3\app\code\Zero\Storelocator\view\frontend\templates\google_reviews.phtml on line 4

line no. 4: $allData = array_slice($allcollection['reviews'], 0, 5, true);

Full code: https://paste.ofcode.org/334bFgXch3bnAWJGaSr5wwh

Function, line no. 3 : getCustomerReview()

Function Code: FUll code : https://paste.ofcode.org/F7Jz4EUa5X9shkZF9MuRu6

function start from line no. 23

Why i am getting this error

Error filtering template: Notice: Trying to access array offset on value of type null in C:\xampp\htdocs\m3\app\code\Zero\Storelocator\view\frontend\templates\google_reviews.phtml on line 4