Error in readRDS(dest) : unknown input format

When I try to invoke packrat::status() or packrat::snapshot()I get the error

Error in readRDS(dest) : unknown input format

and nothing happens.

The packrat version is 0.4.8-1 and these are the information of sessionInfo():

R version 3.4.0 (2017-04-21)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS Sierra 10.12.4

Matrix products: default
BLAS: /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/3.4/Resources/lib/libRlapack.dylib

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

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

other attached packages:
 [1] RPostgreSQL_0.4-1    DBI_0.6-1            testthat_1.0.2      
 [4] forecastHybrid_0.4.0 prophet_0.1.1        Rcpp_0.12.10        
 [7] timekit_0.2.0        hts_5.0              matrixcalc_1.0-3    
[10] Matrix_1.2-10        SparseM_1.77         forecast_8.0        
[13] xts_0.9-7            zoo_1.8-0            dplyr_0.5.0         
[16] purrr_0.2.2          readr_1.1.0          tidyr_0.6.1         
[19] tibble_1.3.0         ggplot2_2.2.1        tidyverse_1.1.1     
[22] lubridate_1.6.0      futile.logger_1.4.3  feather_0.3.1       
[25] doMC_1.3.4           iterators_1.0.8      foreach_1.4.3       
[28] config_0.2          

loaded via a namespace (and not attached):
 [1] lattice_0.20-35      assertthat_0.2.0     packrat_0.4.8-1     
 [4] lmtest_0.9-35        psych_1.7.3.21       R6_2.2.0            
 [7] cellranger_1.1.0     plyr_1.8.4           futile.options_1.0.0
[10] stats4_3.4.0         httr_1.2.1           lazyeval_0.2.0      
[13] readxl_1.0.0         fracdiff_1.4-2       stringr_1.2.0       
[16] foreign_0.8-68       munsell_0.4.3        broom_0.4.2         
[19] compiler_3.4.0       modelr_0.1.0         rstan_2.15.1        
[22] mnormt_1.5-5         nnet_7.3-12          gridExtra_2.2.1     
[25] quadprog_1.5-5       codetools_0.2-15     crayon_1.3.2        
[28] grid_3.4.0           nlme_3.1-131         jsonlite_1.4        
[31] gtable_0.2.0         magrittr_1.5         StanHeaders_2.15.0-1
[34] scales_0.4.1         stringi_1.1.5        reshape2_1.4.2      
[37] tseries_0.10-40      timeDate_3012.100    xml2_1.1.1          
[40] lambda.r_1.1.9       tools_3.4.0          forcats_0.2.0       
[43] hms_0.3              yaml_2.1.14          inline_0.3.14       
[46] colorspace_1.3-2     extraDistr_1.8.5     rvest_0.3.2         
[49] haven_1.0.0         

Reproduce the failure with packrat::status() and packrat::snapshot() using the reported environment, then trace where readRDS(dest) is called. Identify why the destination is not a valid RDS file and verify both commands complete successfully after the fix; the issue does not name a source file or test.