fix: if-else-node handles missing optional file variables (#15693)

api/core/workflow/entities/variable_pool.py

@@ -7,7 +7,7 @@ from pydantic import BaseModel, Field
 
 from core.file import File, FileAttribute, file_manager
 from core.variables import Segment, SegmentGroup, Variable
-from core.variables.segments import FileSegment
+from core.variables.segments import FileSegment, NoneSegment
 from factories import variable_factory
 
 from ..constants import CONVERSATION_VARIABLE_NODE_ID, ENVIRONMENT_VARIABLE_NODE_ID, SYSTEM_VARIABLE_NODE_ID
@@ -131,11 +131,13 @@ class VariablePool(BaseModel):
             if attr not in {item.value for item in FileAttribute}:
                 return None
             value = self.get(selector)
-            if not isinstance(value, FileSegment):
+            if not isinstance(value, (FileSegment, NoneSegment)):
                 return None
-            attr = FileAttribute(attr)
-            attr_value = file_manager.get_attr(file=value.value, attr=attr)
-            return variable_factory.build_segment(attr_value)
+            if isinstance(value, FileSegment):
+                attr = FileAttribute(attr)
+                attr_value = file_manager.get_attr(file=value.value, attr=attr)
+                return variable_factory.build_segment(attr_value)
+            return value
 
         return value