fix: avoid adding empty type only imports

Author: maxholman

lib/process-document.ts

@@ -626,16 +626,20 @@ export async function processOpenApiDocument(
     ],
   });
 
+  const namedImports = [...new Set([...inputTypes, ...outputTypes])];
+
+  if (namedImports.length > 0) {
   mainFile.addImportDeclaration({
     moduleSpecifier: typesModuleSpecifier,
-    namedImports: [...new Set([...inputTypes, ...outputTypes])]
+    namedImports: namedImports
       .filter(<T>(t: T | 'void'): t is T => t !== 'void')
       .map((t) => ({
         name: t.getName(),
       }))
       .sort((a, b) => a.name.localeCompare(b.name)),
     isTypeOnly: true,
   });
+  }
 
   const clientClassDeclaration = mainFile.addClass({
     name: pascalCase(schema.info.title, 'RestClient'),