fix: throw more informative error message when no plot is generated

fix #56

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: rvg
 Type: Package
 Title: R Graphics Devices for 'Office' Vector Graphics Output
-Version: 0.3.3
+Version: 0.3.4.001
 Authors@R: c(
     person("David", "Gohel", role = c("aut", "cre"),
       email = "[email protected]"),
@@ -31,5 +31,5 @@ LinkingTo: Rcpp, gdtools
 Suggests: testthat, grid
 URL: https://ardata-fr.github.io/officeverse/, https://davidgohel.github.io/rvg/
 BugReports: https://github.com/davidgohel/rvg/issues
-RoxygenNote: 7.2.3
+RoxygenNote: 7.3.2
 Roxygen: list(markdown = TRUE)

NEWS.md

@@ -1,3 +1,9 @@
+# rvg 0.3.4
+
+## Issues
+
+* throw more informative error message when no plot is generated
+
 # rvg 0.3.3
 
 ## Issues

R/ph_with_vg.R

@@ -117,6 +117,11 @@ ph_with.dml <- function(x, value, location, ...) {
   )
 
   dml_str <- scan(dml_file, what = "character", quiet = T, sep = "\n", encoding = "UTF-8")
+
+  if (dml_str == "</p:grpSp>") {
+    stop("There was no plot output produced, can not add an empty plot to pptx document.")
+  }
+
   dml_str <- paste(dml_str, collapse = "")
   ph_with(x = x, value = xml2::as_xml_document(dml_str), location = location, ...)
 }