Fix increment=True in write and write_dataframe

TM1py/Services/CellService.py

@@ -1774,7 +1774,7 @@ def write_values_through_cellset(self, mdx: str, values: Iterable, increment: bo
         if increment:
             current_values = self.extract_cellset_values(cellset_id, use_compact_json=True, delete_cellset=False,
                                                          **kwargs)
-            values = (x + (y or None) for x, y in zip(values, current_values))
+            values = (float(x) + float(y or 0) for x, y in zip(values, current_values))
 
         self.update_cellset(cellset_id=cellset_id, values=values, sandbox_name=sandbox_name, **kwargs)
         return changeset