Why is this code outputting clickable URLs for some users, yet not for others?

Question

Some users on the main Tex-chatroom of this site (one using TeX Live) have reported that this (or similar) code IS outputting clickable URLs for them, while for me (using TeXShop), it ISN'T ... What could be the problem?

MWE

\documentclass[a4paper]{article}
\usepackage{xparse, hyperref}

\ExplSyntaxOn
\cs_set_eq:NN
\IfEmptyTF
\tl_if_blank:nTF
\ExplSyntaxOff

\NewDocumentEnvironment {mainentry} { m m m } {%
  \IfEmptyTF{#3}{
First argument returns #1 NO
  }{%
Second argument returns #2 YES
  }%
  }{%
  \href{http://a.beautiful.url/?searchid=#1}{Click on me}%
}

\begin{document}

A) There should be a YES here. OK.

\begin{mainentry}{
first
}{
second
}{
third
}
\end{mainentry}

B) There should be a NO here. OK.

\begin{mainentry}{
first
}{
second
}{
%
}
\end{mainentry}

\end{document}

Answer 1

Just in addition to Manuels comment

\ExplSyntaxOn
\cs_set_eq:NN\IfEmptyTF\tl_if_blank:nTF
\cs_set_eq:NN\Trim\tl_trim_spaces:n
\ExplSyntaxOff

\NewDocumentEnvironment {mainentry} { m m m } {%
  \IfEmptyTF{#3}{
    ... 3 is empty
  }{%
    ... 3 is not empty
  }%
  {%
    \typeout{'#1'}% just to verify
    \edef\temp{\Trim{#1}}
    \typeout{'\temp'}% just to verify
    \expandafter\href\expandafter{http://a.beautiful.url/?searchid=\temp}{Click
      on me}%
  }
}

The rest of the code is the same as in the OPs

Answer 2

The problem here are the spaces. Following User daleif's good suggestion (comment to OP) to check the PDF-output with different viewers, I analyzed the following, when opening the PDF-output from the OP (all on Mac):

• TeXShop 3.88: no sign of any hyperlink
• Safari 11.0: no sign of any hyperlink
• Adobe Acrobat Reader DC 17.012.20098: outputs a clickable hyperlink, namely http://a.beautiful.url/?searchid=%20first%20 instead of http://a.beautiful.url/?searchid=first

Wherein %20 is the percent-encoding of a space.

One example which solves the problem is by changing the syntax layout of e.g.

Original

\begin{mainentry}{
first
}{
second
}{
third
}
\end{mainentry}

into

Solution 1

\begin{mainentry}
{first}
{second}
{third}
\end{mainentry}

Which I actually find very bothersome, because when copy-pasting manual lines (in this case, for example, of content "first", "second", "third"), it's much easier to paste them into empty lines (cf. Original) than to paste them between curly brackets (cf. Solution 1).

To solve at least half of the problem, then, one could propose Solution 2, where by inserting some instances of % we can at least keep one side of the blank lines empty before pasting anything into them:

Solution 2

\begin{mainentry}{%
first%
}{
second%
}{
third%
}
\end{mainentry}