fix: Resolve NPE when McpTool description is null

Author: hemasekhar-p

core/src/main/java/com/google/adk/tools/mcp/AbstractMcpTool.java

@@ -21,6 +21,7 @@
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.adk.tools.BaseTool;
 import com.google.adk.tools.mcp.McpToolException.McpToolDeclarationException;
+import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableMap;
 import com.google.genai.types.FunctionDeclaration;
 import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
@@ -52,7 +53,7 @@ protected AbstractMcpTool(
       Tool mcpTool, T mcpSession, McpSessionManager mcpSessionManager, ObjectMapper objectMapper) {
     super(
         mcpTool == null ? "" : mcpTool.name(),
-        mcpTool == null ? "" : (mcpTool.description().isEmpty() ? "" : mcpTool.description()));
+        mcpTool == null ? "" : (Strings.nullToEmpty(mcpTool.description())));
 
     if (mcpTool == null) {
       throw new IllegalArgumentException("mcpTool cannot be null");

core/src/test/java/com/google/adk/tools/mcp/AbstractMcpToolTest.java

@@ -17,9 +17,13 @@
 package com.google.adk.tools.mcp;
 
 import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.mock;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.common.collect.ImmutableList;
+import io.modelcontextprotocol.client.McpSyncClient;
+import io.modelcontextprotocol.spec.McpSchema;
 import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
 import io.modelcontextprotocol.spec.McpSchema.TextContent;
 import java.util.List;
@@ -56,4 +60,16 @@ public void testWrapCallResult_success() {
     Map<?, ?> contentItem = (Map<?, ?>) content.get(0);
     assertThat(contentItem).containsEntry("text", "success");
   }
+
+  @Test
+  public void instantiateWithToolBuilder_nullDescription_succeeds() {
+    McpSyncClient sessionMock = mock(McpSyncClient.class);
+    McpSessionManager managerMock = mock(McpSessionManager.class);
+    McpSchema.Tool schemaTool = McpSchema.Tool.builder().name("realTool").build();
+
+    McpTool tool = new McpTool(schemaTool, sessionMock, managerMock, objectMapper);
+
+    assertEquals("", tool.description());
+    assertEquals("realTool", tool.name());
+  }
 }