Add test for incompatible 0 column in plots

Author: dmatos2012

lib/matplotlib/axes/_base.py

@@ -514,7 +514,7 @@ def _plot_args(self, tup, kwargs, return_kwargs=False):
         ncx, ncy = x.shape[1], y.shape[1]
         if ncx > 1 and ncy > 1 and ncx != ncy:
             raise ValueError(f"x has {ncx} columns but y has {ncy} columns")
-        if not ncx or not ncy:
+        if ncx == 0 or ncy == 0:
             return []
 
         label = kwargs.get('label')

lib/matplotlib/tests/test_axes.py

@@ -7153,3 +7153,17 @@ def test_artist_sublists():
     # Adding to other lists should produce a regular list.
     assert ax.lines + [1, 2, 3] == [*lines, 1, 2, 3]
     assert [1, 2, 3] + ax.lines == [1, 2, 3, *lines]
+
+
+def test_empty_line_plots():
+    # Incompatible nr columns, plot "nothing"
+    x = np.ones(10)
+    y = np.ones((10, 0))
+    _, ax = plt.subplots()
+    line = ax.plot(x, y)
+    assert len(line) == 0
+
+    # Ensure plot([],[]) creates line
+    _, ax = plt.subplots()
+    line = ax.plot([], [])
+    assert len(line) == 1