Empty tag can cause toRelational() fcn to error with "Can't convert `replace` <character> to match type of `data` <logical>"

[mskyttner]

Thanks for this nice package!

I discovered an issue where an empty tag (see below) can cause toRelational() to fail, see reproducible example below:

# this xml fragment has an empty title tag (nested under relatedItem)
doc_err <- '<xml>
  <titleInfo lang="eng"><title>CreativeBot</title></titleInfo>          
  <relatedItem type="host">
    <titleInfo><title></title></titleInfo>
  </relatedItem>
</xml>
'

# this statement gives an error
doc_err |> xml2relational::toRelational()

# Error in `vec_assign()`:
# ! Can't convert `replace` <character> to match type of `data` <logical>.
# Run `rlang::last_error()` to see where the error occurred.

# this xml fragment is equal to the previous apart except for using a space instead inside the title tag (nested under relatedItem)
doc_ok <- '<xml>
  <titleInfo lang="eng"><title>CreativeBot</title></titleInfo>          
  <relatedItem type="host">
    <titleInfo><title> </title></titleInfo>
  </relatedItem>
</xml>
'

# this statement works ok
doc_ok |> xml2relational::toRelational()

I think https://github.com/jsugarelli/xml2relational/blob/master/R/xml2relational.r#L105 is what is triggering the error.

[mskyttner]

It works better when having using a pairlist() instead of a c() at https://github.com/jsugarelli/xml2relational/blob/master/R/xml2relational.r#L97