add ' 'isNotEmpty

`isNotEmpty` in Dart is used to check if a collection (like a string, list, set, or map) contains any elements, enhancing code readability and consistency.

//Code Example 

List<int> numbers = [1, 2, 3];
if (numbers.isNotEmpty) {
  print("The list is not empty.");
}

Author: mahafujerrahman

data/dart.json

@@ -151,6 +151,10 @@
                     "definition": "একটি স্ট্রিং খালি কিনা",
                     "code": "''.isEmpty"
                 }
+                {
+                    "definition": "একটি স্ট্রিং এ ভ্যালু আছে",
+                    "code": "''.isNotEmpty"
+                }
             ]
         },
         {