minor fix

c++/cavl.hpp

@@ -214,7 +214,7 @@ class Node  // NOSONAR cpp:S1448 cpp:S4963
 private:
     void moveFrom(Node& other) noexcept
     {
-        CAVL_ASSERT(nullptr == up);  // Should not be part of any tree yet.
+        CAVL_ASSERT(!isLinked());  // Should not be part of any tree yet.
 
         up    = other.up;
         lr[0] = other.lr[0];
@@ -338,7 +338,7 @@ auto Node<Derived>::search(Node& origin, const Pre& predicate, const Fac& factor
     bool  r   = false;
     while (n != nullptr)
     {
-        CAVL_ASSERT(nullptr != n->up);
+        CAVL_ASSERT(n->isLinked());
 
         const auto cmp = predicate(*down(n));
         if (0 == cmp)
@@ -486,7 +486,7 @@ void Node<Derived>::remove(Node& origin, const Node* const node) noexcept  // NO
 template <typename Derived>
 auto Node<Derived>::adjustBalance(const bool increment) noexcept -> Node*
 {
-    CAVL_ASSERT(nullptr != up);
+    CAVL_ASSERT(isLinked());
     CAVL_ASSERT(((bf >= -1) && (bf <= +1)));
     Node*      out    = this;
     const auto new_bf = static_cast<std::int8_t>(bf + (increment ? +1 : -1));