fix: only add schema check for newer versions of sls

Author: theburningmonk

lib/index.js

@@ -141,20 +141,23 @@ class ServerlessStepFunctions {
         .then(this.display),
     };
 
-    const stepFunctionsSchema = {
-      type: 'object',
-      properties: {
-        stateMachines: { type: 'object' },
-        validate: { type: 'boolean' },
-        noOutput: { type: 'boolean' },
-        activities: { type: 'array' },
-      },
-      required: ['stateMachines'],
-    };
-    this.serverless.configSchemaHandler.defineTopLevelProperty(
-      'stepFunctions',
-      stepFunctionsSchema,
-    );
+    // relevant since sls v1.78.0
+    if (this.serverless.configSchemaHandler) {
+      const stepFunctionsSchema = {
+        type: 'object',
+        properties: {
+          stateMachines: { type: 'object' },
+          validate: { type: 'boolean' },
+          noOutput: { type: 'boolean' },
+          activities: { type: 'array' },
+        },
+        required: ['stateMachines'],
+      };
+      this.serverless.configSchemaHandler.defineTopLevelProperty(
+        'stepFunctions',
+        stepFunctionsSchema,
+      );
+    }
   }
 
   invoke() {