Make a \newcommand argument optional without consequence

Question

I have this code block in my .cls file -

\newcommand{\ExperienceEntry}[5]{
    \noindent\makebox[\width][l]{#1} \hfill
    \makebox[\width][l]{#2} \\
    \noindent\makebox[\width][l]{#3} \hfill \\
    \indent
    \makebox[\width][l]{\textit{#4}} \vspace{5pt}\\
    \noindent
    \parbox[t][\height][c]{\textwidth}{\small{#5}}
    \vspace{-1pt}
}

How do I make the 3rd argument (#3) optional? By optional I mean if I leave it empty {}, I do not want a gaping space in my document.

For example this is what happens:
This is the .tex code -
and this is the generated document -

I found some relevant documentation about different behaviour depending on the arguments supplied -
Different command definitions with and without optional argument
Optional argument for newcommand?
but i wasn't sure how to use it in my case.
https://stackoverflow.com/questions/1812214/latex-optional-arguments seems most relevant but here one has to define a default behavior whereas I want the default behavior to be to ignore the argument.

Answer 1

This is not an "optional argument" in LaTeX terminology, they use [] not {}. However you can test for the argument being non empty in several ways, for example

\if\relax\detokenize{#2}\relax\else
  \mbox{#2}\\ 
\fi

if #2 is empty this ends up testing \if\relax\relax which is true, in any other case the test will be false, and so #2 will be used. (Note I simplified \makebox to \mbox and removed the spurious space before \\)

---

It looks like you meant to test #3 not #2..

Note

  \noindent\makebox[\width][l]{#3} \hfill \\

you do not need \hfill before \\ and you should not have a space before \hfill and as noted previously you can simply use \mbox, so you can replace this line by

\if\relax\detokenize{#3}\relax\else
  \mbox{#3}\\ 
\fi