Output format from parent.study function

[shbrief]

Hi! I observed the weird format of output from parent.study() function.

parent.study("phs000090")
[1] " 'phs000280.v6.p1" ""

(space) ' in the first element and the empty string in the second element.
Do you know why I got this? Thanks.

> sessionInfo()
R version 3.6.2 (2019-12-12)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS Catalina 10.15.3

Matrix products: default
BLAS:   /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] dbgap2x_1.0 dplyr_0.8.5

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.3        pillar_1.4.3      compiler_3.6.2    bitops_1.0-6      prettyunits_1.1.1 remotes_2.1.1    
 [7] tools_3.6.2       testthat_2.3.2    digest_0.6.25     pkgbuild_1.0.6    pkgload_1.0.2     jsonlite_1.6.1   
[13] memoise_1.1.0     tibble_2.1.3      pkgconfig_2.0.3   rlang_0.4.5       cli_2.0.2         parallel_3.6.2   
[19] curl_4.3          yaml_2.2.1        xfun_0.12         httr_1.4.1        withr_2.1.2       stringr_1.4.0    
[25] knitr_1.28        vctrs_0.2.4       desc_1.2.0        fs_1.3.2          devtools_2.2.2    rprojroot_1.3-2  
[31] tidyselect_1.0.0  data.table_1.12.8 glue_1.3.1        R6_2.4.1          processx_3.4.2    fansi_0.4.1      
[37] XML_3.99-0.3      sessioninfo_1.1.1 callr_3.4.2       purrr_0.3.3       magrittr_1.5      backports_1.1.5  
[43] ps_1.3.2          ellipsis_0.3.0    usethis_1.5.1     assertthat_0.2.1  utf8_1.1.4        stringi_1.4.6    
[49] RCurl_1.98-1.1    crayon_1.3.4