BUG: `Series.map` to tuple values fails for category dtype
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

- [ ] (optional) I have confirmed this bug exists on the master branch of pandas.

---

**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

#### Code Sample, a copy-pastable example

```python
import pandas as pd
s = pd.Series(["a", "a", "b"]).astype("category")
s.map({"a": (1, 2), "b": (3, 4)})
```

#### Problem description

```python-traceback
NotImplementedError: isna is not defined for MultiIndex
```

<details><summary>Full traceback</summary>

```python-traceback
---------------------------------------------------------------------------
NotImplementedError                       Traceback (most recent call last)
<ipython-input-209-1bb58119eb75> in <module>
      1 import pandas as pd
      2 s = pd.Series(["a", "a", "b"]).astype("category")
----> 3 s.map({"a": (1, 2), "b": (3, 4)})

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/series.py in map(self, arg, na_action)
   3907         dtype: object
   3908         """
-> 3909         new_values = super()._map_values(arg, na_action=na_action)
   3910         return self._constructor(new_values, index=self.index).__finalize__(
   3911             self, method="map"

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/base.py in _map_values(self, mapper, na_action)
    901                 # "Union[ExtensionArray, Any]" has no attribute "map"
    902                 # [union-attr]
--> 903                 return self._values.map(mapper)  # type: ignore[union-attr]
    904 
    905             values = self._values

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/arrays/categorical.py in map(self, mapper)
   1196         new_categories = self.categories.map(mapper)
   1197         try:
-> 1198             return self.from_codes(
   1199                 self._codes.copy(), categories=new_categories, ordered=self.ordered
   1200             )

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/arrays/categorical.py in from_codes(cls, codes, categories, ordered, dtype)
    567         Categories (2, object): ['a' < 'b']
    568         """
--> 569         dtype = CategoricalDtype._from_values_or_dtype(
    570             categories=categories, ordered=ordered, dtype=dtype
    571         )

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/dtypes/dtypes.py in _from_values_or_dtype(cls, values, categories, ordered, dtype)
    271             # Note: This could potentially have categories=None and
    272             # ordered=None.
--> 273             dtype = CategoricalDtype(categories, ordered)
    274 
    275         return dtype

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/dtypes/dtypes.py in __init__(self, categories, ordered)
    158 
    159     def __init__(self, categories=None, ordered: Ordered = False):
--> 160         self._finalize(categories, ordered, fastpath=False)
    161 
    162     @classmethod

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/dtypes/dtypes.py in _finalize(self, categories, ordered, fastpath)
    312 
    313         if categories is not None:
--> 314             categories = self.validate_categories(categories, fastpath=fastpath)
    315 
    316         self._categories = categories

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/dtypes/dtypes.py in validate_categories(categories, fastpath)
    505         if not fastpath:
    506 
--> 507             if categories.hasnans:
    508                 raise ValueError("Categorical categories cannot be null")
    509 

pandas/_libs/properties.pyx in pandas._libs.properties.CachedProperty.__get__()

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/indexes/base.py in hasnans(self)
   2193         """
   2194         if self._can_hold_na:
-> 2195             return bool(self._isnan.any())
   2196         else:
   2197             return False

pandas/_libs/properties.pyx in pandas._libs.properties.CachedProperty.__get__()

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/indexes/base.py in _isnan(self)
   2172         """
   2173         if self._can_hold_na:
-> 2174             return isna(self)
   2175         else:
   2176             # shouldn't reach to this condition by checking hasnans beforehand

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/dtypes/missing.py in isna(obj)
    125     Name: 1, dtype: bool
    126     """
--> 127     return _isna(obj)
    128 
    129 

~/miniconda3/envs/seaborn-py38-latest/lib/python3.8/site-packages/pandas/core/dtypes/missing.py in _isna(obj, inf_as_na)
    154     # hack (for now) because MI registers as ndarray
    155     elif isinstance(obj, ABCMultiIndex):
--> 156         raise NotImplementedError("isna is not defined for MultiIndex")
    157     elif isinstance(obj, type):
    158         return False

NotImplementedError: isna is not defined for MultiIndex
```

</details>

#### Expected Output

With an object-typed Series:

```python
import pandas as pd
s = pd.Series(["a", "a", "b"])
s.map({"a": (1, 2), "b": (3, 4)})
```
```
0    (1, 2)
1    (1, 2)
2    (3, 4)
dtype: object
```

#### Output of ``pd.show_versions()``

<details>

```
INSTALLED VERSIONS
------------------
commit           : 2cb96529396d93b46abab7bbc73a208e708c642e
python           : 3.8.5.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 19.6.0
Version          : Darwin Kernel Version 19.6.0: Mon Apr 12 20:57:45 PDT 2021; root:xnu-6153.141.28.1~1/RELEASE_X86_64
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.2.4
numpy            : 1.20.2
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.3.1
setuptools       : 49.6.0.post20210108
Cython           : None
pytest           : 5.4.3
hypothesis       : None
sphinx           : 3.3.1
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.2
IPython          : 7.15.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : 3.4.1
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pyxlsb           : None
s3fs             : None
scipy            : 1.6.3
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None
```

</details>
