How to have condition checking (if command) when use refered parameter of the command line?

Question

In my batch file I have the script:

set myVar=/someLabel:"%1"

I want to write the if command for the above script that have the same meaning as below.

if <%1 not null> {
  myVar=/someLabel:"%1"
} 
else
{
  myVar=""
}

How can I do this? Please help!

[Edit]

The answer from user hfs works for me.

The full details of the if and set command is listed by user Dave Anderson.

Thank you very much all of you!

Answer 1

set myVar=
if not "%1" == "" set myVar=/someLabel:%1

Answer 2

You will need to make sure you have delayed variable expansion enabled or the %1 will always be substituted with what is passed to the batch file regardless of your IF statement.

Here are excellent explanations of the DOS IF and DOS SET commands.