Why does Python think None is a type, and not treat it as null?

Signed-off-by: mmelqin <[email protected]>

Author: MMelQin

monai/deploy/core/domain/dicom_series_selection.py

@@ -9,7 +9,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import Dict, List, Optional
+from typing import Dict, List, Optional, Union
 
 from .dicom_series import DICOMSeries
 from .dicom_study import DICOMStudy
@@ -27,7 +27,7 @@ def __init__(
         self,
         selection_name: str,
         dicom_series: DICOMSeries,
-        image: Image = None,
+        image: Optional[Image] = None,
         metadata: Optional[Dict] = None,
     ) -> None:
         """Creates an instance of this class
@@ -45,7 +45,13 @@ def __init__(
             raise ValueError("Argument dicom_series must be a DICOMSeries object.")
         super().__init__(metadata)
         self._series = dicom_series
-        self._image = image
+
+        if not image:
+            self._image = None
+        elif isinstance(image, Image):
+            self._image = image
+        else:
+            raise ValueError("'image' must be an Image object if not None.")
 
         if not selection_name or not selection_name.strip():
             self._name = str(dicom_series.SeriesInstanceUID)
@@ -61,12 +67,17 @@ def slection_name(self) -> str:
         return self._name
 
     @property
-    def image(self) -> Image:
+    def image(self) -> Union[Image, None]:
         return self._image
 
     @image.setter
-    def image(self, val):
-        self._image = val
+    def image(self, val: Optional[Image]):
+        if not val:
+            self._image = None
+        elif isinstance(val, Image):
+            self._image = val
+        else:
+            raise ValueError("'val' must be an Image object if not None.")
 
 
 class StudySelectedSeries(Domain):

monai/deploy/operators/dicom_series_selector_operator.py

@@ -156,7 +156,7 @@ def filter(self, selection_rules, dicom_study_list, all_matched: bool = False) -
                 series_list = self._select_series(conditions, study, all_matched)
                 if series_list and len(series_list) > 0:
                     for series in series_list:
-                        selected_series = SelectedSeries(selection_name, series)
+                        selected_series = SelectedSeries(selection_name, series, None)  # No Image obj yet.
                         study_selected_series.add_selected_series(selected_series)
 
             if len(study_selected_series.selected_series) > 0:
@@ -182,7 +182,7 @@ def _select_all_series(self, dicom_study_list: List[DICOMStudy]) -> List[StudySe
             for series in study.get_all_series():
                 logging.info(f"Working on series, instance UID: {str(series.SeriesInstanceUID)}")
                 print(f"Working on series, instance UID: {str(series.SeriesInstanceUID)}")
-                selected_series = SelectedSeries("", series)  # No selection name is known or given
+                selected_series = SelectedSeries("", series, None)  # No selection name or Image obj.
                 study_selected_series.add_selected_series(selected_series)
             study_selected_series_list.append(study_selected_series)
         return study_selected_series_list

monai/deploy/operators/dicom_series_to_volume_operator.py

@@ -11,7 +11,7 @@
 
 import copy
 import math
-from typing import Dict, List
+from typing import Dict, List, Union
 
 import numpy as np
 
@@ -38,7 +38,7 @@ def compute(self, op_input: InputContext, op_output: OutputContext, context: Exe
         image = self.convert_to_image(study_selected_series_list)
         op_output.set(image, "image")
 
-    def convert_to_image(self, study_selected_series_list: List[StudySelectedSeries]) -> Image:
+    def convert_to_image(self, study_selected_series_list: List[StudySelectedSeries]) -> Union[Image, None]:
         """Extracts the pixel data from a DICOM Series and other attributes to create an Image object"""
         # For now, only supports the one and only one selected series.
         if not study_selected_series_list or len(study_selected_series_list) < 1: