App: add convenience method DocumentObject::clearExpression()

src/App/DocumentObject.cpp

@@ -949,6 +949,16 @@ void DocumentObject::setExpression(const ObjectIdentifier &path, std::shared_ptr
     ExpressionEngine.setValue(path, expr);
 }
 
+/**
+ * @brief Clear the expression of the object identifier \a path in this document object.
+ * @param path Target object identifier
+ */
+
+void DocumentObject::clearExpression(const ObjectIdentifier & path)
+{
+    setExpression(path, std::shared_ptr<Expression>());
+}
+
 /**
  * @brief Get expression information associated with \a path.
  * @param path Object identifier