[matter_yamltests] Update minLength/maxLength constraints to allow nu…

scripts/py_matter_yamltests/matter_yamltests/constraints.py

@@ -535,7 +535,8 @@ def _is_double(self, value):
 
 class _ConstraintMinLength(BaseConstraint):
     def __init__(self, context, min_length):
-        super().__init__(context, types=[str, bytes, list])
+        super().__init__(context, types=[
+            str, bytes, list], is_null_allowed=True)
         self._min_length = min_length
 
     def check_response(self, value, value_type_name) -> bool:
@@ -547,7 +548,8 @@ def get_reason(self, value, value_type_name) -> str:
 
 class _ConstraintMaxLength(BaseConstraint):
     def __init__(self, context, max_length):
-        super().__init__(context, types=[str, bytes, list])
+        super().__init__(context, types=[
+            str, bytes, list], is_null_allowed=True)
         self._max_length = max_length
 
     def check_response(self, value, value_type_name) -> bool:

src/app/tests/suites/TestConstraints.yaml

@@ -359,6 +359,34 @@ tests:
       arguments:
           value: ""
 
+    # Tests for NULLABLE_CHAR_STRING attribute
+
+    - label: "Write attribute NULLABLE_CHAR_STRING Value"
+      command: "writeAttribute"
+      attribute: "nullable_char_string"
+      arguments:
+          value: null
+
+    - label: "Read attribute NULLABLE_CHAR_STRING Value MinLength Constraints"
+      command: "readAttribute"
+      attribute: "nullable_char_string"
+      response:
+          constraints:
+              minLength: 5
+
+    - label: "Read attribute NULLABLE_CHAR_STRING Value MaxLength Constraints"
+      command: "readAttribute"
+      attribute: "nullable_char_string"
+      response:
+          constraints:
+              maxLength: 20
+
+    - label: "Write attribute NULLABLE_CHAR_STRING Value Back to Default Value"
+      command: "writeAttribute"
+      attribute: "nullable_char_string"
+      arguments:
+          value: ""
+
     # Tests for hasValue attribute
 
     - label: "Read attribute NULLABLE_INT8U Default Value"

src/app/tests/suites/include/ConstraintsChecker.h

@@ -79,12 +79,36 @@ class ConstraintsChecker
         return CheckConstraintMinLength(itemName, current.size(), expected);
     }
 
+    template <typename T>
+    bool CheckConstraintMinLength(const char * itemName, const chip::app::DataModel::Nullable<chip::Span<T>> & current,
+                                  uint64_t expected)
+    {
+        if (current.IsNull())
+        {
+            return true;
+        }
+
+        return CheckConstraintMinLength(itemName, current.Value(), expected);
+    }
+
     template <typename T>
     bool CheckConstraintMaxLength(const char * itemName, const chip::Span<T> & current, uint64_t expected)
     {
         return CheckConstraintMaxLength(itemName, current.size(), expected);
     }
 
+    template <typename T>
+    bool CheckConstraintMaxLength(const char * itemName, const chip::app::DataModel::Nullable<chip::Span<T>> & current,
+                                  uint64_t expected)
+    {
+        if (current.IsNull())
+        {
+            return true;
+        }
+
+        return CheckConstraintMaxLength(itemName, current.Value(), expected);
+    }
+
     template <typename T>
     bool CheckConstraintMinLength(const char * itemName, const chip::app::DataModel::DecodableList<T> & current, uint64_t expected)
     {