Add fallback message for blank tool execution errors

Auto-cherry-pick to 1.0.x
Fixes #4518

Signed-off-by: cho-thinkfree-com <cho@thinkfree.com>

Author: cho-thinkfree-com

spring-ai-model/src/main/java/org/springframework/ai/tool/execution/DefaultToolExecutionExceptionProcessor.java

@@ -72,9 +72,13 @@ public String process(ToolExecutionException exception) {
 		if (this.alwaysThrow) {
 			throw exception;
 		}
-		logger.debug("Exception thrown by tool: {}. Message: {}", exception.getToolDefinition().name(),
-				exception.getMessage());
-		return exception.getMessage();
+		String message = exception.getMessage();
+		if (message == null || message.isBlank()) {
+			message = "Exception occurred in tool: " + exception.getToolDefinition().name() + " ("
+					+ cause.getClass().getSimpleName() + ")";
+		}
+		logger.debug("Exception thrown by tool: {}. Message: {}", exception.getToolDefinition().name(), message);
+		return message;
 	}
 
 	public static Builder builder() {

spring-ai-model/src/test/java/org/springframework/ai/tool/execution/DefaultToolExecutionExceptionProcessorTests.java

@@ -60,6 +60,28 @@ void processReturnsMessage() {
 		assertThat(result).isEqualTo(this.toolException.getMessage());
 	}
 
+	@Test
+	void processReturnsFallbackMessageWhenNull() {
+		DefaultToolExecutionExceptionProcessor processor = DefaultToolExecutionExceptionProcessor.builder().build();
+
+		ToolExecutionException exception = new ToolExecutionException(this.toolDefinition, new IllegalStateException());
+
+		String result = processor.process(exception);
+
+		assertThat(result).isEqualTo("Exception occurred in tool: toolName (IllegalStateException)");
+	}
+
+	@Test
+	void processReturnsFallbackMessageWhenBlank() {
+		DefaultToolExecutionExceptionProcessor processor = DefaultToolExecutionExceptionProcessor.builder().build();
+
+		ToolExecutionException exception = new ToolExecutionException(this.toolDefinition, new RuntimeException(" "));
+
+		String result = processor.process(exception);
+
+		assertThat(result).isEqualTo("Exception occurred in tool: toolName (RuntimeException)");
+	}
+
 	@Test
 	void processAlwaysThrows() {
 		DefaultToolExecutionExceptionProcessor processor = DefaultToolExecutionExceptionProcessor.builder()