spring-projects/spring-ai · error · IllegalArgumentException

Bean must not be null

Error message

Bean must not be null

What it means

The builder's validate() method (in AbstractMcpLoggingMethodCallback's Builder) throws IllegalArgumentException when bean is null at build() time. The callback needs the bean instance on which to invoke the annotated logging method.

Source

Thrown at mcp/mcp-annotations/src/main/java/org/springframework/ai/mcp/annotation/method/logging/AbstractMcpLoggingMethodCallback.java:241

		 * @param loggingConsumer The logging consumer annotation
		 * @return This builder
		 */
		@SuppressWarnings("unchecked")
		public T loggingConsumer(McpLogging loggingConsumer) {
			// No additional configuration needed from the annotation at this time
			return (T) this;
		}

		/**
		 * Validate the builder state.
		 * @throws IllegalArgumentException if the builder state is invalid
		 */
		protected void validate() {
			if (this.method == null) {
				throw new IllegalArgumentException("Method must not be null");
			}
			if (this.bean == null) {
				throw new IllegalArgumentException("Bean must not be null");
			}
		}

		/**
		 * Build the callback.
		 * @return A new callback instance
		 */
		public abstract R build();

	}

}

View on GitHub (pinned to 98a7beda4f)

Solutions

1. Call bean(...) with the instance that declares the @McpLogging method before build()
2. Ensure the bean is instantiated (e.g. retrieved from the application context) and non-null
3. If using DI, verify component scanning actually creates the handler bean

Example fix

// before
Callback cb = new Builder().method(m).build(); // throws
// after
Callback cb = new Builder().method(m).bean(logHandler).build();

Object handler = applicationContext.getBean(LogHandler.class);
if (handler == null) { throw new IllegalStateException("bean must be set before build()"); }
new Builder().method(m).bean(handler).build();

static boolean hasBean(Object bean) { return bean != null; }

When it happens

Trigger: Calling build() on a logging callback Builder after setting method(...) but without calling bean(Object).

Common situations: Manual registration outside a DI container where no bean instance is supplied; bean factory returned null; copy-pasted builder setup omitted the bean call.

Related errors

• Method must not be null
• Method must not be null
• Request must not be null
• Request must not be null
• Method must not be null

AI-assisted analysis of spring-projects/spring-ai@98a7beda4f (2026-09-11). Data as JSON: /api/errors/a2f56e93d67a3ba4. Report an issue: GitHub.