Join fails with PanicException instead of ColumnNotFoundError

[jankislinger]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

# join.py
import polars as pl

a = pl.DataFrame({"x": [1, 2, 3]})
b = pl.DataFrame({"y": [1, 2, 3]})
a.join(b, on="y")

> uv run --with 'polars==1.12.0' join.py
Traceback (most recent call last):
  File "/home/jan/phd/clustering/join.py", line 5, in <module>
    a.join(b, on="y")
  File "/home/jan/phd/clustering/.venv/lib/python3.12/site-packages/polars/dataframe/frame.py", line 7150, in join
    .collect(_eager=True)
     ^^^^^^^^^^^^^^^^^^^^
  File "/home/jan/phd/clustering/.venv/lib/python3.12/site-packages/polars/lazyframe/frame.py", line 2055, in collect
    return wrap_df(ldf.collect(callback))
                   ^^^^^^^^^^^^^^^^^^^^^
polars.exceptions.ColumnNotFoundError: "y" not found

> uv run --with 'polars==1.13.0' join.py
thread '<unnamed>' panicked at crates/polars-plan/src/plans/conversion/join.rs:126:14:
called `Option::unwrap()` on a `None` value
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Traceback (most recent call last):
  File "/home/jan/phd/clustering/join.py", line 5, in <module>
    a.join(b, on="y")
  File "/home/jan/.cache/uv/archive-v0/Vi6ISUc8Vikk9vWM4Og84/lib/python3.12/site-packages/polars/dataframe/frame.py", line 7151, in join
    .collect(_eager=True)
     ^^^^^^^^^^^^^^^^^^^^
  File "/home/jan/.cache/uv/archive-v0/Vi6ISUc8Vikk9vWM4Og84/lib/python3.12/site-packages/polars/lazyframe/frame.py", line 2021, in collect
    return wrap_df(ldf.collect(callback))
                   ^^^^^^^^^^^^^^^^^^^^^
pyo3_runtime.PanicException: called `Option::unwrap()` on a `None` value

> uv run --with 'polars==1.13.1' join.py
thread '<unnamed>' panicked at crates/polars-plan/src/plans/conversion/join.rs:126:14:
called `Option::unwrap()` on a `None` value
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Traceback (most recent call last):
  File "/home/jan/phd/clustering/join.py", line 5, in <module>
    a.join(b, on="y")
  File "/home/jan/.cache/uv/archive-v0/DlBEEtqNl5PBvMKH3DEWW/lib/python3.12/site-packages/polars/dataframe/frame.py", line 7151, in join
    .collect(_eager=True)
     ^^^^^^^^^^^^^^^^^^^^
  File "/home/jan/.cache/uv/archive-v0/DlBEEtqNl5PBvMKH3DEWW/lib/python3.12/site-packages/polars/lazyframe/frame.py", line 2021, in collect
    return wrap_df(ldf.collect(callback))
                   ^^^^^^^^^^^^^^^^^^^^^
pyo3_runtime.PanicException: called `Option::unwrap()` on a `None` value

Log output

No response

Issue description

When joining on column that doesn't exist, version 1.13 throws panic exception instead of the ColumnNotFoundError it throws with version 1.12. I see the bug in Python so marking it as such, but I think the bug might be in Rust instead.

Expected behavior

All three versions should throw the same error ColumnNotFoundError

Installed versions

--------Version info---------
Polars:              1.13.1
Index type:          UInt32
Platform:            Linux-6.8.0-48-generic-x86_64-with-glibc2.39
Python:              3.12.3 (main, Sep 11 2024, 14:17:37) [GCC 13.2.0]
LTS CPU:             False

----Optional dependencies----
adbc_driver_manager  <not installed>
altair               <not installed>
cloudpickle          <not installed>
connectorx           <not installed>
deltalake            <not installed>
fastexcel            <not installed>
fsspec               2024.10.0
gevent               <not installed>
great_tables         <not installed>
matplotlib           <not installed>
nest_asyncio         <not installed>
numpy                2.1.3
openpyxl             <not installed>
pandas               <not installed>
pyarrow              <not installed>
pydantic             <not installed>
pyiceberg            <not installed>
sqlalchemy           <not installed>
torch                2.5.1+cu124
xlsx2csv             <not installed>
xlsxwriter           <not installed>