Is ssl_dhparam necessary for nginx when client use the cipher DHE-RSA-AES256-SHA256

In Nginx I set ssl_ciphers as DHE-RSA-AES256-SHA256 and send a https request by openssl command "openssl s_client -connect 1.1.1.1:443 -cipher DHE-RSA-AES128-SHA256 -state". There is one error log in nginx says

"484815 SSL_do_handshake() failed (SSL: error:1408A0C1:SSL routines:ssl3_get_client_hello:no shared cipher) while SSL handshaking ".

So I add ssl_dhparam dhparam.pem in nginx.conf. The dhparam.pem is generated by openssl.

This time no error appeared.

I'm confused if the dhparam file is necessary when nginx need to support the DHE cipher.

Thank you very much!