fix: read_csv for empty lines (#11924)

crates/polars-io/src/csv/utils.rs

@@ -306,6 +306,10 @@ pub fn infer_file_schema_inner(
         // keep track so that we can determine the amount of bytes read
         end_ptr = line.as_ptr() as usize + line.len();
 
+        if line.is_empty() {
+            continue;
+        }
+
         if let Some(c) = comment_char {
             // line is a comment -> skip
             if line[0] == c {

py-polars/tests/unit/io/test_csv.py

@@ -527,6 +527,30 @@ def test_empty_bytes() -> None:
     assert_frame_equal(df, pl.DataFrame())
 
 
+def test_empty_line_with_single_column() -> None:
+    df = pl.read_csv(
+        b"a\n\nb\n",
+        new_columns=["A"],
+        has_header=False,
+        comment_char="#",
+        use_pyarrow=False,
+    )
+    expected = pl.DataFrame({"A": ["a", None, "b"]})
+    assert_frame_equal(df, expected)
+
+
+def test_empty_line_with_multiple_columns() -> None:
+    df = pl.read_csv(
+        b"a,b\n\nc,d\n",
+        new_columns=["A", "B"],
+        has_header=False,
+        comment_char="#",
+        use_pyarrow=False,
+    )
+    expected = pl.DataFrame({"A": ["a", "c"], "B": ["b", "d"]})
+    assert_frame_equal(df, expected)
+
+
 def test_csv_quote_char() -> None:
     expected = pl.DataFrame(
         [