QST: should pandas series isin raise an exception with a nested sequence? 
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#### Question about pandas

Using a nested structure in series isin() does not rasie an exception, instead no match is found? Should this pass silently? 

```python
# Your code here, if applicable
test = pd.DataFrame({'a': [1,2,3]})
test['a'].isin([1])

0     True
1    False
2    False

test['a'].isin([[1]])

0    False
1    False
2    False

pd.__version__
'0.25.0'

```
