Cleanup: Clang-Tidy modernize-use-nullptr

Replace `NULL` with `nullptr` in C++ code.

No functional changes.

source/blender/gpu/opengl/gl_uniform_buffer.cc

@@ -61,7 +61,7 @@ void GLUniformBuf::init()
 
   glGenBuffers(1, &ubo_id_);
   glBindBuffer(GL_UNIFORM_BUFFER, ubo_id_);
-  glBufferData(GL_UNIFORM_BUFFER, size_in_bytes_, NULL, GL_DYNAMIC_DRAW);
+  glBufferData(GL_UNIFORM_BUFFER, size_in_bytes_, nullptr, GL_DYNAMIC_DRAW);
 
   debug::object_label(GL_UNIFORM_BUFFER, ubo_id_, name_);
 }
@@ -97,7 +97,7 @@ void GLUniformBuf::bind(int slot)
     this->init();
   }
 
-  if (data_ != NULL) {
+  if (data_ != nullptr) {
     this->update(data_);
     MEM_SAFE_FREE(data_);
   }