From 9a8c9f8a327573e6ad4ce0aeea8285541291bb1c Mon Sep 17 00:00:00 2001
From: wlandau <will.landau@gmail.com>
Date: Sun, 6 Jan 2019 20:05:06 -0500
Subject: [PATCH] Fix #658

---
 R/exec-meta.R | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/R/exec-meta.R b/R/exec-meta.R
index 7135b5f0a..6f4a47e7c 100644
--- a/R/exec-meta.R
+++ b/R/exec-meta.R
@@ -90,6 +90,9 @@ dependency_hash <- function(target, config) {
   if (is_imported(target, config)) {
     deps <- c(deps, x$file_in, x$knitr_in)
   }
+  if (!length(deps)) {
+    return("")
+  }
   deps <- unlist(deps)
   deps <- as.character(deps)
   deps <- unique(deps)
@@ -110,6 +113,9 @@ input_file_hash <- function(
 ) {
   deps <- config$layout[[target]]$deps_build
   files <- sort(unique(as.character(c(deps$file_in, deps$knitr_in))))
+  if (!length(files)) {
+    return("")
+  }
   out <- vapply(
     X = files,
     FUN = file_hash,
@@ -132,6 +138,9 @@ output_file_hash <- function(
 ) {
   deps <- config$layout[[target]]$deps_build
   files <- sort(unique(as.character(deps$file_out)))
+  if (!length(files)) {
+    return("")
+  }
   out <- vapply(
     X = files,
     FUN = file_hash,