Don't promise that passing a NULL to mbedtls_mpi_read_string works
@@ -412,8 +412,7 @@ int mbedtls_mpi_read_string( mbedtls_mpi *X, int radix, const char *s );
* \param X The source MPI. This must point to an initialized MPI.
* \param radix The numeric base of the output string.
* \param buf The buffer to write the string to. This must be writable
- * buffer of length \p buflen Bytes. It May be \c NULL if
- * `buflen == 0`.
+ * buffer of length \p buflen Bytes.
* \param buflen The available size in Bytes of \p buf.
* \param olen The address at which to store the length of the string
* written, including the final \c NULL byte. This must
