Name the everyday media type extensions, refuse an emptied table, and cut the false register claim

data-import/tsv.py

@@ -5,12 +5,14 @@ from pathlib import Path
 
 
 def write(path, columns, rows):
-    """Write the rows as a TSV; every cell must be non-empty and free of tabs, newlines and braces."""
+    """Write the rows as a TSV; the table needs a row, and every cell must be non-empty and free of tabs, newlines and braces."""
     lines = ["\t".join(columns)]
     for row in rows:
         cells = [str(row[c]) for c in columns]
         if not all(cells) or any(re.search(r"[\t\n{}]", c) for c in cells):
             raise ValueError(f"{path}: a cell is empty or holds a tab, newline or brace: {row}")
         lines.append("\t".join(cells))
+    if len(lines) < 2:
+        raise ValueError(f"{path}: has no rows below its header; a table is at least two rows")
     Path(path).write_text("\n".join(lines) + "\n", encoding="utf-8")
     print(f"{path}: {len(lines) - 1} rows", file=sys.stderr)