`Transformer.to_json()` returns `None` for valid CRS pair

[T90REAL]

Code Sample, a copy-pastable example if possible

from pyproj import Transformer

t = Transformer.from_crs("EPSG:4258", "EPSG:32633")
print(t)
print(t.to_json())
print(t.to_json_dict())

unavailable until proj_trans is called
None
Traceback (most recent call last):
  File "/data/src/test.py", line 6, in <module>
    print(t.to_json_dict())     # TypeError: the JSON object must be str, bytes or bytearray, not NoneType
          ^^^^^^^^^^^^^^^^
  File "/home/hdd/miniconda3/envs/py312/lib/python3.12/site-packages/pyproj/transformer.py", line 1157, in to_json_dict
    return self._transformer.to_json_dict()
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "pyproj/_crs.pyx", line 477, in pyproj._crs.Base.to_json_dict
  File "/home/hdd/miniconda3/envs/py312/lib/python3.12/json/__init__.py", line 339, in loads
    raise TypeError(f'the JSON object must be str, bytes or bytearray, '
TypeError: the JSON object must be str, bytes or bytearray, not NoneType

Problem description

Creating a Transformer via Transformer.from_crs("EPSG:4258", "EPSG:32633") yields an object whose to_json() method returns None. The docstring promise a JSON string, so downstream code that expects a str crashes (e.g., json.loads).

Expected Output

The return should be a valid json str.

Environment Information

• Output from: pyproj -v

 pyproj info:
     pyproj: 3.7.2
 PROJ (runtime): 9.5.1
 PROJ (compiled): 9.5.1
   data dir: /home/hdd/PBT-AgentSys/src/envs/pyproj_env/lib/python3.12/site-packages/pyproj/proj_dir/share/proj
 user_data_dir: /home/.local/share/proj
 PROJ DATA (recommended version): 1.20
 PROJ Database: 1.4
 EPSG Database: v11.022 [2024-11-05]
 ESRI Database: ArcGIS Pro 3.4 [2024-11-04]
 IGNF Database: 3.1.0 [2019-05-24]

 System:
     python: 3.12.12 | packaged by Anaconda, Inc. | (main, Oct 21 2025, 20:16:04) [GCC 11.2.0]
 executable: /home/hdd/PBT-AgentSys/src/envs/pyproj_env/bin/python3
    machine: Linux-5.15.0-139-generic-x86_64-with-glibc2.31

 Python deps:
    certifi: 2025.10.5
     Cython: None
 setuptools: None
        pip: 25.0.1

Installation method

pip (inside a virtual environment)

[T90REAL]

from pyproj import Transformer

t = Transformer.from_crs("EPSG:4326", "EPSG:27700")
print(t.transform(-0.1278, 51.5074))
print(t.to_wkt())                     # None  <-- should be a WKT string
print(t.to_wkt(pretty=True))          # None  <-- same issue

The same problem.