Fix issue Azure#3217 (Azure#3233)

- If ApiId is not provided, generate it.

Author: solankisamir

src/ResourceManager/ApiManagement/Commands.ApiManagement.ServiceManagement/Commands/ImportAzureApiManagementApi.cs

@@ -83,6 +83,8 @@ public class ImportAzureApiManagementApi : AzureApiManagementCmdletBase
 
         public override void ExecuteApiManagementCmdlet()
         {
+            ApiId = ApiId ?? Guid.NewGuid().ToString("N");
+
             if (ParameterSetName.Equals(FromLocalFile))
             {
                 Client.ApiImportFromFile(Context, ApiId, SpecificationFormat, SpecificationPath, Path, WsdlServiceName, WsdlEndpointName);