Domain name cant be set to blank

[xbipin]

while setting up pfsense we need to put a domain name and this is used in dhcp clients as dns suffix, now the problem is when on dhcp, there is a local sql server on the lan and clients r not able to connect to the sql instance, did a packet capture and it shows that the sql server rejects the user by saying unknown user, now if i set static ip on the client machine then the dns suffix becomes blank and in that case the client can connect to the sql server. i tried to set a blank domain in pfsense but it wouldn't allow that, is there any way to over come this?