diff --git a/Modules/Bridge/NumPy/include/itkPyBuffer.hxx b/Modules/Bridge/NumPy/include/itkPyBuffer.hxx
index e5853eb1019..1618a2bf2ef 100644
--- a/Modules/Bridge/NumPy/include/itkPyBuffer.hxx
+++ b/Modules/Bridge/NumPy/include/itkPyBuffer.hxx
@@ -28,7 +28,7 @@ template <class TImage>
 PyObject *
 PyBuffer<TImage>::_GetArrayViewFromImage(ImageType * image)
 {
-  PyObject * memoryView = NULL;
+  PyObject * memoryView = nullptr;
   Py_buffer  pyBuffer{};
 
   Py_ssize_t len = 1;
@@ -58,7 +58,7 @@ PyBuffer<TImage>::_GetArrayViewFromImage(ImageType * image)
   len *= numberOfComponents;
   len *= sizeof(ComponentType);
 
-  res = PyBuffer_FillInfo(&pyBuffer, NULL, itkImageBuffer, len, 0, PyBUF_CONTIG);
+  res = PyBuffer_FillInfo(&pyBuffer, nullptr, itkImageBuffer, len, 0, PyBUF_CONTIG);
   memoryView = PyMemoryView_FromBuffer(&pyBuffer);
 
   PyBuffer_Release(&pyBuffer);
@@ -71,8 +71,8 @@ auto
 PyBuffer<TImage>::_GetImageViewFromArray(PyObject * arr, PyObject * shape, PyObject * numOfComponent)
   -> const OutputImagePointer
 {
-  PyObject * shapeseq = NULL;
-  PyObject * item = NULL;
+  PyObject * shapeseq = nullptr;
+  PyObject * item = nullptr;
 
   Py_buffer pyBuffer{};
 
@@ -111,7 +111,7 @@ PyBuffer<TImage>::_GetImageViewFromArray(PyObject * arr, PyObject * shape, PyObj
   }
 
   bool isFortranContiguous = false;
-  if (pyBuffer.strides != NULL && pyBuffer.itemsize == pyBuffer.strides[0])
+  if (pyBuffer.strides != nullptr && pyBuffer.itemsize == pyBuffer.strides[0])
   {
     isFortranContiguous = true;
   }
diff --git a/Modules/Bridge/NumPy/include/itkPyVectorContainer.hxx b/Modules/Bridge/NumPy/include/itkPyVectorContainer.hxx
index c89c39bd120..46a16a9661e 100644
--- a/Modules/Bridge/NumPy/include/itkPyVectorContainer.hxx
+++ b/Modules/Bridge/NumPy/include/itkPyVectorContainer.hxx
@@ -27,7 +27,7 @@ template <typename TElementIdentifier, typename TElement>
 PyObject *
 PyVectorContainer<TElementIdentifier, TElement>::_array_view_from_vector_container(VectorContainerType * vector)
 {
-  PyObject * memoryView = NULL;
+  PyObject * memoryView = nullptr;
   Py_buffer  pyBuffer{};
 
   int res = 0;
@@ -45,7 +45,7 @@ PyVectorContainer<TElementIdentifier, TElement>::_array_view_from_vector_contain
   Py_ssize_t len = vector->Size();
   len *= sizeof(DataType);
 
-  res = PyBuffer_FillInfo(&pyBuffer, NULL, vectorBuffer, len, 0, PyBUF_CONTIG);
+  res = PyBuffer_FillInfo(&pyBuffer, nullptr, vectorBuffer, len, 0, PyBUF_CONTIG);
   memoryView = PyMemoryView_FromBuffer(&pyBuffer);
 
   PyBuffer_Release(&pyBuffer);
@@ -58,9 +58,9 @@ auto
 PyVectorContainer<TElementIdentifier, TElement>::_vector_container_from_array(PyObject * arr, PyObject * shape) -> const
   typename VectorContainerType::Pointer
 {
-  PyObject * obj = NULL;
-  PyObject * shapeseq = NULL;
-  PyObject * item = NULL;
+  PyObject * obj = nullptr;
+  PyObject * shapeseq = nullptr;
+  PyObject * item = nullptr;
 
   Py_buffer pyBuffer{};
 
diff --git a/Modules/Bridge/NumPy/include/itkPyVnl.hxx b/Modules/Bridge/NumPy/include/itkPyVnl.hxx
index 8fdca392f60..85da91664c4 100644
--- a/Modules/Bridge/NumPy/include/itkPyVnl.hxx
+++ b/Modules/Bridge/NumPy/include/itkPyVnl.hxx
@@ -27,7 +27,7 @@ template <class TElement>
 PyObject *
 PyVnl<TElement>::_GetArrayViewFromVnlVector(VectorType * vector)
 {
-  PyObject * memoryView = NULL;
+  PyObject * memoryView = nullptr;
   Py_buffer  pyBuffer{};
 
   int res = 0;
@@ -45,7 +45,7 @@ PyVnl<TElement>::_GetArrayViewFromVnlVector(VectorType * vector)
   Py_ssize_t len = vector->size();
   len *= sizeof(DataType);
 
-  res = PyBuffer_FillInfo(&pyBuffer, NULL, vectorBuffer, len, 0, PyBUF_CONTIG);
+  res = PyBuffer_FillInfo(&pyBuffer, nullptr, vectorBuffer, len, 0, PyBUF_CONTIG);
   memoryView = PyMemoryView_FromBuffer(&pyBuffer);
 
   PyBuffer_Release(&pyBuffer);
@@ -57,9 +57,9 @@ template <class TElement>
 auto
 PyVnl<TElement>::_GetVnlVectorFromArray(PyObject * arr, PyObject * shape) -> const VectorType
 {
-  PyObject * obj = NULL;
-  PyObject * shapeseq = NULL;
-  PyObject * item = NULL;
+  PyObject * obj = nullptr;
+  PyObject * shapeseq = nullptr;
+  PyObject * item = nullptr;
 
   Py_buffer pyBuffer{};
 
@@ -104,7 +104,7 @@ template <class TElement>
 PyObject *
 PyVnl<TElement>::_GetArrayViewFromVnlMatrix(MatrixType * matrix)
 {
-  PyObject * memoryView = NULL;
+  PyObject * memoryView = nullptr;
   Py_buffer  pyBuffer{};
 
   int res = 0;
@@ -122,7 +122,7 @@ PyVnl<TElement>::_GetArrayViewFromVnlMatrix(MatrixType * matrix)
   Py_ssize_t len = matrix->size();
   len *= sizeof(DataType);
 
-  res = PyBuffer_FillInfo(&pyBuffer, NULL, matrixBuffer, len, 0, PyBUF_CONTIG);
+  res = PyBuffer_FillInfo(&pyBuffer, nullptr, matrixBuffer, len, 0, PyBUF_CONTIG);
   memoryView = PyMemoryView_FromBuffer(&pyBuffer);
 
   PyBuffer_Release(&pyBuffer);
@@ -134,9 +134,9 @@ template <class TElement>
 auto
 PyVnl<TElement>::_GetVnlMatrixFromArray(PyObject * arr, PyObject * shape) -> const MatrixType
 {
-  PyObject * obj = NULL;
-  PyObject * shapeseq = NULL;
-  PyObject * item = NULL;
+  PyObject * obj = nullptr;
+  PyObject * shapeseq = nullptr;
+  PyObject * item = nullptr;
 
   Py_buffer pyBuffer{};