change format of annotation_snippet column for compatibility with Python client

Change-Id: Id6bd21cf45fe01d4646495e9d7a3ffde11f13d14
diff --git a/R/KorAPQuery.R b/R/KorAPQuery.R
index 765e4bf..6dd5b44 100644
--- a/R/KorAPQuery.R
+++ b/R/KorAPQuery.R
@@ -1228,7 +1228,7 @@
   }
 
   if (overwrite || !existing_types$annotation_snippet) {
-    df$annotation_snippet <- replicate(nrows, NA, simplify = FALSE)
+  	df$annotation_snippet <- rep(NA_character_, nrows)  # Fixed line
   }
 
   # Initialize timing for ETA calculation