Always deserialize simpleTypes (for example, attribute values) as Some(…)

[Mingun]

This also matches behavior for elements (so we will be more consistent, see changed tests), where <a/> is always will be Some(...) because tag is present.

Fixes #671. @francisdb, FYI

[codecov-commenter]

Codecov Report

Merging #672 (ab8d519) into master (569ac22) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##           master     #672      +/-   ##
==========================================
- Coverage   65.31%   65.31%   -0.01%     
==========================================
  Files          38       38              
  Lines       17839    17837       -2     
==========================================
- Hits        11652    11650       -2     
  Misses       6187     6187              

Flag	Coverage Δ
unittests	65.31% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
src/de/simple_type.rs	93.89% <100.00%> (-0.02%)	⬇️

[francisdb]

I guess this keeps deserializing missing optional attributes as None?

[Mingun]

Yes:

Rust	Attribute	Element
None	missed	missed
Some("")	a=""	<a/>
Some("a")	a="a"	<a>a</a>

See those tests:

quick-xml/tests/serde-issues.rs

Line 13 in ab8d519

mod issue252 {

[francisdb]

I see, the tricky part is in the element.