add pseudocode to handle empty version string in OnChanOpenInit

docs/ibc/middleware/develop.md

@@ -93,24 +93,33 @@ func (im IBCModule) OnChanOpenInit(
     counterparty channeltypes.Counterparty,
     version string,
 ) (string, error) {
-    // try to unmarshal JSON-encoded version string and pass
-    // the app-specific version to app callback.
-    // otherwise, pass version directly to app callback.
-    metadata, err := Unmarshal(version)
-    if err != nil {
-        // Since it is valid for fee version to not be specified,
-        // the above middleware version may be for another middleware.
-        // Pass the entire version string onto the underlying application.
-        return im.app.OnChanOpenInit(
-            ctx,
-            order,
-            connectionHops,
-            portID,
-            channelID,
-            channelCap,
-            counterparty,
-            version,
-        )
+    if version != "" {
+        // try to unmarshal JSON-encoded version string and pass
+        // the app-specific version to app callback.
+        // otherwise, pass version directly to app callback.
+        metadata, err := Unmarshal(version)
+        if err != nil {
+            // Since it is valid for fee version to not be specified,
+            // the above middleware version may be for another middleware.
+            // Pass the entire version string onto the underlying application.
+            return im.app.OnChanOpenInit(
+                ctx,
+                order,
+                connectionHops,
+                portID,
+                channelID,
+                channelCap,
+                counterparty,
+                version,
+            )
+        }
+    else {
+        metadata = {
+            // set middleware version to default value
+            MiddlewareVersion: defaultMiddlewareVersion,
+            // allow application to return its default version
+            AppVersion: "",
+        }
     }
 
     doCustomLogic()
@@ -152,8 +161,6 @@ func OnChanOpenTry(
     counterparty channeltypes.Counterparty,
     counterpartyVersion string,
 ) (string, error) {
-    doCustomLogic()
-
     // try to unmarshal JSON-encoded version string and pass
     // the app-specific version to app callback.
     // otherwise, pass version directly to app callback.
@@ -171,6 +178,8 @@ func OnChanOpenTry(
         )
     }
 
+    doCustomLogic()
+
     // Call the underlying application's OnChanOpenTry callback.
     // The try callback must select the final app-specific version string and return it.
     appVersion, err := app.OnChanOpenTry(