Fix error message (#267)

Author: AlexHolly

lib/index.js

@@ -43,15 +43,11 @@ class SwaggerParser extends $RefParser {
       let schema = await super.parse(args.path, args.schema, args.options);
 
       if (schema.swagger) {
-        // Verify that the parsed object is a Swagger API
-        if (schema.swagger === undefined || schema.info === undefined || schema.paths === undefined) {
-          throw ono.syntax(`${args.path || args.schema} is not a valid Swagger API definition`);
-        }
-        else if (typeof schema.swagger === "number") {
+        if (typeof schema.swagger === "number") {
           // This is a very common mistake, so give a helpful error message
           throw ono.syntax('Swagger version number must be a string (e.g. "2.0") not a number.');
         }
-        else if (typeof schema.info.version === "number") {
+        else if (schema.info && typeof schema.info.version === "number") {
           // This is a very common mistake, so give a helpful error message
           throw ono.syntax('API version number must be a string (e.g. "1.0.0") not a number.');
         }
@@ -60,11 +56,7 @@ class SwaggerParser extends $RefParser {
         }
       }
       else {
-        // Verify that the parsed object is a Openapi API
-        if (schema.openapi === undefined || schema.info === undefined) {
-          throw ono.syntax(`${args.path || args.schema} is not a valid Openapi API definition`);
-        }
-        else if (schema.paths === undefined) {
+        if (schema.paths === undefined) {
           if (supported31Versions.indexOf(schema.openapi) !== -1) {
             if (schema.webhooks === undefined) {
               throw ono.syntax(`${args.path || args.schema} is not a valid Openapi API definition`);
@@ -78,7 +70,7 @@ class SwaggerParser extends $RefParser {
           // This is a very common mistake, so give a helpful error message
           throw ono.syntax('Openapi version number must be a string (e.g. "3.0.0") not a number.');
         }
-        else if (typeof schema.info.version === "number") {
+        else if (schema.info && typeof schema.info.version === "number") {
           // This is a very common mistake, so give a helpful error message
           throw ono.syntax('API version number must be a string (e.g. "1.0.0") not a number.');
         }