Fix pick channels crash when _orig_units is None (mne-tools#11314)

Picking/reordering channels built {k: v for ... in self._orig_units.items()}
unconditionally, raising AttributeError when _orig_units is None (as produced
by some readers / RawArray flows). Guard for a falsy _orig_units. Adds a test.

Author: CedricConday

doc/changes/dev/11314.bugfix.rst

@@ -0,0 +1 @@
+Fix a crash (``AttributeError`` on ``NoneType``) when picking channels on a :class:`~mne.io.Raw` whose ``_orig_units`` is ``None``, by `Cedric Conday`_.

mne/channels/channels.py

@@ -646,9 +646,10 @@ def _pick_drop_channels(self, idx, *, verbose=None):
 
         if isinstance(self, BaseRaw):
             self.annotations._prune_ch_names(self.info, on_missing="ignore")
-            self._orig_units = {
-                k: v for k, v in self._orig_units.items() if k in self.ch_names
-            }
+            if self._orig_units:
+                self._orig_units = {
+                    k: v for k, v in self._orig_units.items() if k in self.ch_names
+                }
 
         self._pick_projs()
         return self

mne/channels/tests/test_channels.py

@@ -696,3 +696,17 @@ def test_combine_channels_metadata():
     good = dict(foo=[0, 1, 3, 4], bar=[5, 2])  # good grad and mag
     combined_epochs = combine_channels(epochs, good)
     pd.testing.assert_frame_equal(epochs.metadata, combined_epochs.metadata)
+
+
+def test_pick_channels_orig_units_none():
+    """Picking channels must not crash when _orig_units is None (gh-11314)."""
+    import numpy as np
+
+    import mne
+
+    info = mne.create_info(["Fp1", "Fp2", "F3", "F4"], 100.0, "eeg")
+    raw = mne.io.RawArray(np.zeros((4, 100)), info)
+    raw._orig_units = None  # the state reported by some readers / RawArray flows
+    raw.pick(["Fp1", "Fp2"])  # previously raised AttributeError on None.items()
+    assert raw.ch_names == ["Fp1", "Fp2"]
+    assert raw._orig_units is None