Add fallback message for blank tool execution errors

Fixes #4518 Signed-off-by: cho-thinkfree-com <cho@thinkfree.com> (cherry picked from commit f2d57cc)

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

@@ -59,6 +59,28 @@ 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()