message: Drag and Drop: Allow NULL payload (since type only can be useful).
diff: @@ -11223,7 +11223,7 @@ bool ImGui::SetDragDropPayload(const char* type, const void* data, size_t data_s
  IM_ASSERT(type != NULL);
  IM_ASSERT(strlen(type) < IM_ARRAYSIZE(payload.DataType)); // Payload type can be at most 8 characters longs
  - IM_ASSERT(data != NULL && data_size > 0);
  + IM_ASSERT((data != NULL && data_size > 0) || (data == NULL && data_size == 0));
  IM_ASSERT(cond == ImGuiCond_Always || cond == ImGuiCond_Once);
  IM_ASSERT(payload.SourceId != 0); // Not called between BeginDragDropSource() and EndDragDropSource()
  