diff --git a/modules/swagger-codegen/src/main/java/io/swagger/codegen/v3/utils/URLPathUtil.java b/modules/swagger-codegen/src/main/java/io/swagger/codegen/v3/utils/URLPathUtil.java
index ee4149bde1a..ea14e55bdbe 100644
--- a/modules/swagger-codegen/src/main/java/io/swagger/codegen/v3/utils/URLPathUtil.java
+++ b/modules/swagger-codegen/src/main/java/io/swagger/codegen/v3/utils/URLPathUtil.java
@@ -19,6 +19,7 @@ public class URLPathUtil {
 
     protected static final Logger LOGGER = LoggerFactory.getLogger(URLPathUtil.class);
     public static String DEFAULT_PATH = "/";
+    public static String DEFAULT_PORT = "8080";
     public static final String LOCAL_HOST = "http://localhost:8080";
 
     public static URL getServerURL(OpenAPI openAPI) {
@@ -107,7 +108,7 @@ private static String replaceServerVarsWthDefaultValues(String url, ServerVariab
                 .stream()
                 .collect(Collectors.toMap(
                     Map.Entry::getKey,
-                    e -> e.getValue().getDefault()));
+                    e -> e.getValue().getDefault() != null ? e.getValue().getDefault() : DEFAULT_PORT));
             return StrSubstitutor.replace(url, defaultValues, "{", "}");
         }
         return url;
diff --git a/modules/swagger-codegen/src/test/java/io/swagger/codegen/v3/utils/URLPathUtilTest.java b/modules/swagger-codegen/src/test/java/io/swagger/codegen/v3/utils/URLPathUtilTest.java
index 0f1c6fb5c51..c4bc5693ff8 100644
--- a/modules/swagger-codegen/src/test/java/io/swagger/codegen/v3/utils/URLPathUtilTest.java
+++ b/modules/swagger-codegen/src/test/java/io/swagger/codegen/v3/utils/URLPathUtilTest.java
@@ -150,6 +150,6 @@ public void testVariableSubstitutionMissingDefault() throws Exception {
         // No default for port, resulting URL is invalid.
         URL url = URLPathUtil.getServerURL(openAPI, config);
 
-        Assert.assertNull(url);
+        Assert.assertEquals(new URL("http://myhost:8080/mypath"), url);
     }
 }