gh-138005: Document that CSV skipinitialspace=True and delimiter=' ' require quotation for empty fields

Doc/library/csv.rst

@@ -469,6 +469,23 @@ Dialects support the following attributes:
    When :const:`True`, spaces immediately following the *delimiter* are ignored.
    The default is :const:`False`.
 
+   .. note::
+
+      When combining ``delimiter=' '`` (a space) with ``skipinitialspace=True``,
+      the writer must quote empty fields.
+
+      If an unquoted empty field would be emitted (for example writing ``''`` or
+      values that become empty like :data:`None` under some quoting modes),
+      :class:`writer` raises :exc:`csv.Error`. Quoting (the default
+      :data:`QUOTE_MINIMAL` is sufficient) avoids this error.
+
+      Example::
+
+          >>> import csv, io
+          >>> buf = io.StringIO()
+          >>> w = csv.writer(buf, delimiter=' ', skipinitialspace=True,
+          ...                 quoting=csv.QUOTE_NONE)
+          >>> w.writerow(['', 'x'])  # raises csv.Error
 
 .. attribute:: Dialect.strict
 
@@ -636,7 +653,7 @@ done::
 .. rubric:: Footnotes
 
 .. [1] If ``newline=''`` is not specified, newlines embedded inside quoted fields
-   will not be interpreted correctly, and on platforms that use ``\r\n`` linendings
+   will not be interpreted correctly, and on platforms that use ``\r\n`` line endings
    on write an extra ``\r`` will be added.  It should always be safe to specify
    ``newline=''``, since the csv module does its own
    (:term:`universal <universal newlines>`) newline handling.