fix(pandas): handle struct columns with NA elements

ibis/backends/pandas/execution/structs.py

@@ -1,7 +1,7 @@
 """Pandas backend execution of struct fields and literals."""
 
 import collections
-import operator
+import functools
 
 import pandas as pd
 from pandas.core.groupby import SeriesGroupBy
@@ -15,17 +15,30 @@ def execute_node_struct_field_dict(op, data, **kwargs):
     return data[op.field]
 
 
+@execute_node.register(ops.StructField, type(None))
+def execute_node_struct_field_none(op, data, **kwargs):
+    return None
+
+
 @execute_node.register(ops.StructField, pd.Series)
 def execute_node_struct_field_series(op, data, **kwargs):
     field = op.field
-    return data.map(operator.itemgetter(field)).rename(field)
+    return data.map(functools.partial(_safe_getter, field=field)).rename(field)
+
+
+def _safe_getter(value, field: str):
+    try:
+        return value[field]
+    except TypeError:
+        return value
 
 
 @execute_node.register(ops.StructField, SeriesGroupBy)
 def execute_node_struct_field_series_group_by(op, data, **kwargs):
     field = op.field
+
     return (
-        data.obj.map(operator.itemgetter(field))
+        data.obj.map(functools.partial(_safe_getter, field=field))
         .rename(field)
         .groupby(data.grouper.groupings)
     )