Function concat( s1, s2, s3, s4 )

Description:
Concatenates four strings. In most cases the same effect can be achieved by writing s1+s2+s3+s4, but blank values can sometimes appear as the string "null" if you do it like that.
Parameters:
s1 (String)
first string
s2 (String)
second string
s3 (String)
third string
s4 (String)
fourth string
Return Value (String):
s1 followed by s2 followed by s3 followed by s4
Example:
concat("a", "b", "c", "d") = "abcd"
Signature:
String concat(String, String, String, String)