fix: make highlight null-safe

Author: aminya

lib/adapters/code-highlight-adapter.ts

@@ -24,11 +24,11 @@ export default class CodeHighlightAdapter {
     serverCapabilities: ServerCapabilities,
     editor: TextEditor,
     position: Point
-  ): Promise<Range[] | null> {
+  ): Promise<Range[]> {
     assert(serverCapabilities.documentHighlightProvider, "Must have the documentHighlight capability")
     const highlights = await connection.documentHighlight(Convert.editorToTextDocumentPositionParams(editor, position))
     if (!highlights) {
-      return null
+      return []
     }
     return highlights.map((highlight) => {
       return Convert.lsRangeToAtomRange(highlight.range)