@@ -62,7 +62,7 @@ public A2AClientHTTPError(int code, String message, Object data) {
         Assert.checkNotNullParam("message", message);
         this.code = code;
         this.message = message;
-        this.responseBody = data instanceof String s ? s : null;
+        this.responseBody = data instanceof String s ? s : "";
     }
 
     /**
Original file line number	Diff line number	Diff line change
`@@ -62,7 +62,7 @@ public A2AClientHTTPError(int code, String message, Object data) {`
`62`	`62`	`Assert.checkNotNullParam("message", message);`
`63`	`63`	`this.code = code;`
`64`	`64`	`this.message = message;`
`65`		`- this.responseBody = data instanceof String s ? s : null;`
	`65`	`+ this.responseBody = data instanceof String s ? s : "";`
`66`	`66`	`}`
`67`	`67`
`68`	`68`	`/**`