Fall back to session check if metadata is missing

`getNotebookType()` has two ways to determine the language. If the
metadata check fails, it falls through to the current session check.
Previously, if metadata was `null`, the method would return early.

src/formatter.ts

@@ -93,38 +93,41 @@ export class JupyterlabNotebookCodeFormatter extends JupyterlabCodeFormatter {
   }
 
   private getNotebookType(): string | null {
+    // If there is no current notebook, there is nothing to do
     if (!this.notebookTracker.currentWidget) {
       return null;
     }
 
+    // first, check the notebook's metadata for language info
     const metadata =
       this.notebookTracker.currentWidget.content.model?.sharedModel?.metadata;
 
-    if (!metadata) {
-      return null;
-    }
-
-    // prefer kernelspec language
-    if (
-      metadata.kernelspec &&
-      metadata.kernelspec.language &&
-      typeof metadata.kernelspec.language === 'string'
-    ) {
-      return metadata.kernelspec.language.toLowerCase();
-    }
+    if (metadata) {
+      // prefer kernelspec language
+      if (
+        metadata.kernelspec &&
+        metadata.kernelspec.language &&
+        typeof metadata.kernelspec.language === 'string'
+      ) {
+        return metadata.kernelspec.language.toLowerCase();
+      }
 
-    // otherwise, check language info code mirror mode
-    if (metadata.language_info && metadata.language_info.codemirror_mode) {
-      const mode = metadata.language_info.codemirror_mode;
-      if (typeof mode === 'string') {
-        return mode.toLowerCase();
-      } else if (typeof mode.name === 'string') {
-        return mode.name.toLowerCase();
+      // otherwise, check language info code mirror mode
+      if (
+        metadata.language_info &&
+        metadata.language_info.codemirror_mode
+      ) {
+        const mode = metadata.language_info.codemirror_mode;
+        if (typeof mode === 'string') {
+          return mode.toLowerCase();
+        } else if (typeof mode.name === 'string') {
+          return mode.name.toLowerCase();
+        }
       }
     }
 
-    // finally, try to get the language from the current session's kernel spec
-    const sessionContext = this.notebookTracker.currentWidget?.sessionContext;
+    // in the absence of metadata, look in the current session's kernel spec
+    const sessionContext = this.notebookTracker.currentWidget.sessionContext;
     const kernelName = sessionContext?.session?.kernel?.name;
     if (kernelName) {
       const specs = sessionContext.specsManager.specs?.kernelspecs;