Prune empty import

Author: simonihmig

__testfixtures__/native-dom/prune-import.input.js

@@ -0,0 +1 @@
+import { click } from 'ember-native-dom-helpers';

__testfixtures__/native-dom/prune-import.output.js

@@ -0,0 +1 @@
+import { click } from '@ember/test-helpers';

lib/transforms/native-dom/migrate-imports.js

@@ -69,7 +69,12 @@ function transform(file, api) {
       newSpecifiers.push(specifier);
     }
   });
-  oldSpecifiers.replace(newSpecifiers);
+
+  if (newSpecifiers.length > 0) {
+    oldSpecifiers.replace(newSpecifiers);
+  } else {
+    nativeDomImportStatement.remove();
+  }
 
   addImportStatement(newImports);
   writeImportStatements(j, root);