fix: handle root exceptions in McpToolCallback

- Sync and Async McpToolCallback can now handle exceptions where cause == null instead of throwing a NPE. Signed-off-by: Daniel Garnier-Moiroux <git@garnier.wf>

Author: Kehrlann

mcp/common/src/main/java/org/springframework/ai/mcp/AsyncMcpToolCallback.java

@@ -122,7 +122,7 @@ public String call(String functionInput) {
 }).block();
 }
 catch (Exception ex) {
-throw new ToolExecutionException(this.getToolDefinition(), ex.getCause());
+throw new ToolExecutionException(this.getToolDefinition(), ex);
 }
 
 }

mcp/common/src/main/java/org/springframework/ai/mcp/SyncMcpToolCallback.java

@@ -131,7 +131,7 @@ public String call(String functionInput) {
 }
 catch (Exception ex) {
 logger.error("Exception while tool calling: ", ex);
-throw new ToolExecutionException(this.getToolDefinition(), ex.getCause());
+throw new ToolExecutionException(this.getToolDefinition(), ex);
 }
 
 }

mcp/common/src/test/java/org/springframework/ai/mcp/AsyncMcpToolCallbackTest.java

@@ -0,0 +1,38 @@
+package org.springframework.ai.mcp;
+
+import io.modelcontextprotocol.client.McpAsyncClient;
+import io.modelcontextprotocol.spec.McpSchema;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import org.springframework.ai.tool.execution.ToolExecutionException;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+class AsyncMcpToolCallbackTest {
+
+@Mock
+private McpAsyncClient mcpClient;
+
+@Mock
+private McpSchema.Tool tool;
+
+@Test
+void callShouldHandleExceptions() {
+when(this.tool.name()).thenReturn("testTool");
+var clientInfo = new McpSchema.Implementation("testClient", "1.0.0");
+when(this.mcpClient.getClientInfo()).thenReturn(clientInfo);
+when(this.mcpClient.callTool(any(McpSchema.CallToolRequest.class))).thenThrow(new RuntimeException("Testing tool error"));
+
+AsyncMcpToolCallback callback = new AsyncMcpToolCallback(this.mcpClient, this.tool);
+assertThatThrownBy(() -> callback.call("{\"param\":\"value\"}"))
+.isInstanceOf(ToolExecutionException.class)
+.rootCause()
+.hasMessage("Testing tool error");
+}
+
+}

mcp/common/src/test/java/org/springframework/ai/mcp/SyncMcpToolCallbackTests.java

@@ -29,8 +29,10 @@
 import org.mockito.junit.jupiter.MockitoExtension;
 
 import org.springframework.ai.chat.model.ToolContext;
+import org.springframework.ai.tool.execution.ToolExecutionException;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
@@ -94,4 +96,18 @@ void callShouldIgnoreToolContext() {
 assertThat(response).isNotNull();
 }
 
+@Test
+void callShouldWrapExceptions() {
+when(this.tool.name()).thenReturn("testTool");
+var clientInfo = new Implementation("testClient", "1.0.0");
+when(this.mcpClient.getClientInfo()).thenReturn(clientInfo);
+when(this.mcpClient.callTool(any(CallToolRequest.class))).thenThrow(new RuntimeException("Testing tool error"));
+
+SyncMcpToolCallback callback = new SyncMcpToolCallback(this.mcpClient, this.tool);
+assertThatThrownBy(() -> callback.call("{\"param\":\"value\"}"))
+.isInstanceOf(ToolExecutionException.class)
+.rootCause()
+.hasMessage("Testing tool error");
+}
+
 }