fix: empty servers threw an error

Fix #3

Author: philsturgeon

__tests__/one-api-version-per-document.test.ts

@@ -53,6 +53,35 @@ testRule("one-api-version-per-document", [
 		errors: [],
 	},
 
+  {
+    name: "valid case: no servers defined",
+    document: {
+      openapi: "3.1.0",
+      info: { version: "1.0" },
+    },
+    errors: [],
+  },
+  
+  {
+    name: "valid case: empty servers defined",
+    document: {
+      openapi: "3.1.0",
+      info: { version: "1.0" },
+      servers: [],
+    },
+    errors: [],
+  },
+  
+  {
+    name: "valid case: weird servers defined",
+    document: {
+      openapi: "3.1.0",
+      info: { version: "1.0" },
+      servers: {},
+    },
+    errors: [],
+  },
+
 	{
 		name: "invalid: multiple versions in directory",
 		document: {

src/functions/onlyOneServerVersion.ts

@@ -8,12 +8,16 @@ export default createRulesetFunction({
   options: {
     type: ['null'],
   },
-}, (targetVal: any) => {
+}, (targetVal: Array<any>) => {
+
+  if (! Array.isArray(targetVal)) {
+    return [];
+  }
 
   const versionsMatches = targetVal.map(({ url }: any) => url.match(/([\\.|\\/|](v|version)?[0-9]{1,3}(?:\/)?)/i)[0]);
 
   // If there are fewer than two versions mentioned there cannot be multiple versions
-  if (versionsMatches < 2) {
+  if (versionsMatches.length < 2) {
     return [];
   }