fix(csv): handle trailing empty field at EOF without newline in COPY FROM

src/processor/operator/persistent/reader/csv/base_csv_reader.cpp

@@ -518,6 +518,14 @@ BaseCSVReader::parse_result_t BaseCSVReader::parseCSV(Driver& driver) {
                 return {curRowIdx, numErrors};
             }
             column++;
+        } else if (column > 0) {
+            // File ends right after a delimiter with an empty trailing field.
+            // Without this, a row like "a,b," (no trailing newline) loses its last
+            // empty field and undercounts columns, causing "expected N, got N-1".
+            if (!addValue(driver, curRowIdx, column, std::string_view{}, escapePositions)) {
+                return {curRowIdx, numErrors};
+            }
+            column++;
         }
         if (column > 0) {
             curRowIdx += driver.addRow(curRowIdx, column,

test/test_files/csv/issues_trailing_empty_field_eof.test

@@ -0,0 +1,19 @@
+-DATASET CSV empty
+
+--
+
+# Regression test for the fix in ffce93a49c306806a546b3cd368bc50849c87688
+# "fix(csv): handle trailing empty field at EOF without newline"
+#
+# When a CSV file ends with a row like "a,b," (no trailing newline, last field
+# empty), the parser used to drop the empty field, causing "expected N values
+# per row, but got N-1". The fix adds an else-if branch in final_state to emit
+# the empty value when column > 0.
+-CASE TrailingEmptyFieldAtEOF
+-STATEMENT CREATE NODE TABLE t(A STRING, B STRING, C STRING, PRIMARY KEY(A));
+---- ok
+-STATEMENT COPY t FROM "${LBUG_ROOT_DIRECTORY}/dataset/csv-edge-case-tests/trailing-empty-field-eof.csv";
+---- ok
+-STATEMENT MATCH (t:t) RETURN t.*;
+---- 1
+a|b|