Fixed crash on no 'externalContext' in md files.

libs/externalContext.js

@@ -1,6 +1,10 @@
 export function parseExternalContext(externalContext) {
-    // Remove start and end tag
-    externalContext = externalContext.replace(/%%-\n|-%%\n/g, "")
+    // If there's no external context, return nothing.
+    if (!externalContext)
+        return {}
+
+    // Remove start and end tag       ↓ Only care about the first "externalConext"
+    externalContext = externalContext[0].replace(/%%-\n|-%%\n/g, "")
 
     let parsedContext = {}
     externalContext.split("\n").forEach(line => {

libs/siteRenderer.js

@@ -24,7 +24,7 @@ export function mdRenderer(path) {
 
     // Separate the actual markdown from potential 'externalContext'
     const externalMarkdown = externalMarkdownFile.replace(/^%%-\n[\S\s]*-%%\n/, "").replace(/```\w*[\s\S]*?```/g, match => match.replace(/ /g, "•"))
-    const externalContext = externalMarkdownFile.match(/^%%-\n[\S\s]*-%%\n/)[0]
+    const externalContext = externalMarkdownFile.match(/^%%-\n[\S\s]*-%%\n/)
 
     // Pre-render the template for analysis during context generation.
     const prerenderedNjk = njk.renderString(njkFile, { externalMarkdown })