Add Dart Queue isNotEmpty documentation

docs/content/dart/concepts/queue/terms/isNotEmpty/isNotEmpty.md

@@ -0,0 +1,84 @@
+---
+Title: '.isNotEmpty'
+Description: 'Returns true if the queue is not empty.'
+Subjects:
+  - 'Code Foundations'
+  - 'Computer Science'
+Tags:
+  - 'Dart'
+  - 'Queue'
+  - 'Properties'
+CatalogContent:
+  - 'learn-dart'
+  - 'paths/computer-science'
+---
+
+In Dart, the **`.isNotEmpty`** property checks whether a `Queue` contains one or more elements. It returns `true` if the queue has at least one element and `false` if the queue is empty. This property is commonly used in conditional logic before accessing or removing elements from a queue.
+
+## Syntax
+
+```pseudo
+queue.isNotEmpty
+```
+
+**Parameters:**
+
+- This property takes no parameters.
+
+**Return value:**
+
+Returns a boolean value:
+
+- `true` if the queue contains at least one element
+- `false` if the queue is empty
+
+## Example 1: Checking Queue State
+
+This example demonstrates how `.isNotEmpty` can be used to verify whether a queue has elements before performing operations on it:
+
+```dart
+import 'dart:collection';
+
+void main() {
+  Queue<int> numbers = Queue();
+
+  numbers.add(10);
+  numbers.add(20);
+
+  print(numbers.isNotEmpty);
+}
+```
+
+The output of this code is:
+
+```shell
+true
+```
+
+## Example 2: Using `.isNotEmpty` in a Loop
+
+This example shows how `.isNotEmpty` can be used to safely process and remove elements from a queue until it becomes empty:
+
+```dart
+import 'dart:collection';
+
+void main() {
+  Queue<String> tasks = Queue();
+
+  tasks.addAll(['Task A', 'Task B', 'Task C']);
+
+  while (tasks.isNotEmpty) {
+    print('Processing ${tasks.removeFirst()}');
+  }
+}
+```
+
+The output of this code is:
+
+```shell
+Processing Task A
+Processing Task B
+Processing Task C
+```
+
+This pattern ensures that elements are only removed while the queue contains items, preventing runtime errors.