How can i check if shape:[] is null in json with php

I have a json object like this :

{"Techne":{"@Version":"2.2","Author":"ZeuX","Name":"","PreviewImage":"","ProjectName":"","ProjectType":"","Description":"","DateCreated":"","Models":[{"Model":{"GlScale":"1,1,1","Name":"","TextureSize":"1,1","@texture":"texture.png","BaseClass":"ModelBase","Geometry":{"Folder":[],"Shape":[],"Piece":[],"Null":[]}}}]}}

How can I check if the array Shape:[] is empty with PHP I only know how to do it with JavaScript but this matter needs PHP to be used how can I do it?