Store version option instance instead of just name

Storing the Option instance of the version option instead of just its
.attributeName() (_versionOptionName) is meaningful for cases when other
properties of the instance need to be accessed (not currently the case,
but could be in the future).

lib/command.js

@@ -79,7 +79,7 @@ class Command extends EventEmitter {
     this._helpConfiguration = {};
 
     this._version = undefined;
-    this._versionOptionName = undefined;
+    this._versionOption = undefined;
   }
 
   /**
@@ -1562,10 +1562,11 @@ Expecting one of '${allowedValues.join("', '")}'`);
       // Preserve original behaviour so backwards compatible when still using properties
       const result = {};
       const len = this.options.length;
+      const versionOptionName = this._versionOption?.attributeName();
 
       for (let i = 0; i < len; i++) {
         const key = this.options[i].attributeName();
-        result[key] = key === this._versionOptionName ? this._version : this[key];
+        result[key] = key === versionOptionName ? this._version : this[key];
       }
       return result;
     }
@@ -1821,10 +1822,9 @@ Expecting one of '${allowedValues.join("', '")}'`);
     this._version = str;
     flags = flags || '-V, --version';
     description = description || 'output the version number';
-    const versionOption = this.createOption(flags, description);
-    this._versionOptionName = versionOption.attributeName();
-    this.options.push(versionOption);
-    this.on('option:' + versionOption.name(), () => {
+    this._versionOption = this.createOption(flags, description);
+    this.options.push(this._versionOption);
+    this.on('option:' + this._versionOption.name(), () => {
       this._outputConfiguration.writeOut(`${str}\n`);
       this._exit(0, 'commander.version', str);
     });