separate stanzas using empty line 1

[w5000]

hello

input file contains many user stanzas in password file but some stanzas are not as expected separated by empty line (like in example below guest4,5,6 stanzas are not separated).
how to easily correct it in whole file to be able "grep -p ^username:" in this file?

I tested:
sed '/^.*:$/{x;p;x;}'
and
sed '/^.*:/{x;p;x;}'

I hope ":" will never happen in any type of password = and lastupdate =, flags = attributes.
can it be prevented extra in above command(s)?

guest3:
        password = s.gtrwrwr545.
        lastupdate = 1142355052
        flags =

guest4:
        password = z.GwvrwrrwjA
        lastupdate = 1142355057
        flags =
guest5:
        password = 
guest6:
        password = F0wrwrwrwrF.
        lastupdate = 1250607014

guest7:
        password = yPorwrehfghI
        lastupdate = 1250607020
        flags =

 

[PHV]

What about this ?
awk 'NR>1 && nf && /:$/{printf "\n"}{nf=NF;print}' /path/to/input

Hope This Helps, PH.
FAQ219-2884
FAQ181-2886

 

[PHV]

A more secure way:
awk 'NR>1 && nf && /^[^ \t]*:$/{printf "\n"}{nf=NF;print}' /path/to/input

Hope This Helps, PH.
FAQ219-2884
FAQ181-2886

 

[PHV]

w5000, just to know, did you try my suggestion ?