have a default elliptic curve
RFC4492 requires that when an implementation does not send the supported elliptic curves extension the server should assume that any elliptic curve is supported. That although it could pose an issue in the future due to incompatibilities on assumptions, it is to accommodate clients which send an SSLv2 client hello that cannot attach any extensions. For that we should ensure that when no extension is sent, the secp256r1 curve (most compatible) is assumed to be available. This can be tested with tlsfuzzers' test 'ECDHE w/o extension'.
Edited by Nikos Mavrogiannopoulos