Fix trailing newline

__tests__/changelog-updater.test.ts

@@ -779,6 +779,7 @@ test('should keep the trailing newline', async () => {
 - Update \`package\` from v1 to v2 ([#123](https://github.com/owner/repo/pull/123))
 
 ## [v0.9.0]
+
 `)
 })
 

src/changelog-updater.ts

@@ -180,7 +180,7 @@ function writeEntry(
   // Push a copy of the last line to the end of the contents and include the line-ending
   // It will be overwritten when we re-write all the contents
   const lastLine = contents[contents.length - 1]
-  const length = contents.push(`${lastLine}${EOL}`)
+  const length = contents.push(lastLine)
 
   // Copy the contents from the last line up until the line of the entry we want to write
   for (let i = length - 1; i > lineNumber; i--) {
@@ -190,6 +190,12 @@ function writeEntry(
   // Write the entry
   contents[lineNumber] = changelogEntry
 
+  // If the last line was empty, assume it is a trailing newline
+  // Append an additional newline to write the trailing newline
+  if (lastLine == '') {
+    contents.push('')
+  }
+
   // Write the contents out, joining with EOL
   fs.writeFileSync(changelogPath, contents.join(EOL))
 }