diff --git a/src/ArduinoJson/Array/ArrayImpl.hpp b/src/ArduinoJson/Array/ArrayImpl.hpp
index 47467e04..3fdcb554 100644
--- a/src/ArduinoJson/Array/ArrayImpl.hpp
+++ b/src/ArduinoJson/Array/ArrayImpl.hpp
@@ -20,6 +20,9 @@ inline ArrayImpl::iterator ArrayImpl::at(size_t index) const {
 }
 
 inline VariantData* ArrayImpl::addElement() {
+  if (!data_)
+    return nullptr;
+  ARDUINOJSON_ASSERT(resources_ != nullptr);
   auto slot = resources_->allocVariant();
   if (!slot)
     return nullptr;
diff --git a/src/ArduinoJson/Collection/CollectionImpl.hpp b/src/ArduinoJson/Collection/CollectionImpl.hpp
index 70a615bd..ef8247e1 100644
--- a/src/ArduinoJson/Collection/CollectionImpl.hpp
+++ b/src/ArduinoJson/Collection/CollectionImpl.hpp
@@ -32,6 +32,9 @@ inline CollectionImpl::iterator CollectionImpl::createIterator() const {
 }
 
 inline void CollectionImpl::appendOne(Slot<VariantData> slot) {
+  ARDUINOJSON_ASSERT(data_ != nullptr);
+  ARDUINOJSON_ASSERT(resources_ != nullptr);
+
   if (data_->tail != NULL_SLOT) {
     auto tail = resources_->getVariant(data_->tail);
     tail->setNext(slot.id());
@@ -44,6 +47,9 @@ inline void CollectionImpl::appendOne(Slot<VariantData> slot) {
 
 inline void CollectionImpl::appendPair(Slot<VariantData> key,
                                        Slot<VariantData> value) {
+  ARDUINOJSON_ASSERT(data_ != nullptr);
+  ARDUINOJSON_ASSERT(resources_ != nullptr);
+
   key->setNext(value.id());
 
   if (data_->tail != NULL_SLOT) {
diff --git a/src/ArduinoJson/Object/ObjectImpl.hpp b/src/ArduinoJson/Object/ObjectImpl.hpp
index 9d4ee5cf..41f6d0a3 100644
--- a/src/ArduinoJson/Object/ObjectImpl.hpp
+++ b/src/ArduinoJson/Object/ObjectImpl.hpp
@@ -47,6 +47,10 @@ inline void ObjectImpl::removeMember(TAdaptedString key) {
 
 template <typename TAdaptedString>
 inline VariantData* ObjectImpl::addMember(TAdaptedString key) {
+  if (!data_)
+    return nullptr;
+  ARDUINOJSON_ASSERT(resources_ != nullptr);
+
   auto keySlot = resources_->allocVariant();
   if (!keySlot)
     return nullptr;
@@ -64,6 +68,10 @@ inline VariantData* ObjectImpl::addMember(TAdaptedString key) {
 }
 
 inline VariantData* ObjectImpl::addPair(VariantData** value) {
+  if (!data_)
+    return nullptr;
+  ARDUINOJSON_ASSERT(resources_ != nullptr);
+
   auto keySlot = resources_->allocVariant();
   if (!keySlot)
     return nullptr;