fix(anthropic): Add streaming parameter-less tool support

models/spring-ai-anthropic/src/main/java/org/springframework/ai/anthropic/api/AnthropicApi.java

@@ -1060,8 +1060,7 @@ public List<ContentBlockStartEvent.ContentBlockToolUse> getToolContentBlocks() {
 		  * @return True if the event is empty, false otherwise.
 		*/
 		public boolean isEmpty() {
-			return (this.index == null || this.id == null || this.name == null
-					|| !StringUtils.hasText(this.partialJson));
+			return (this.index == null || this.id == null || this.name == null);
 		}
 
 		ToolUseAggregationEvent withIndex(Integer index) {

models/spring-ai-anthropic/src/test/java/org/springframework/ai/anthropic/client/AnthropicChatClientMethodInvokingFunctionCallbackIT.java

@@ -19,18 +19,23 @@
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.stream.Collectors;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.condition.EnabledIfEnvironmentVariable;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import org.springframework.ai.anthropic.AnthropicTestConfiguration;
 import org.springframework.ai.chat.client.ChatClient;
 import org.springframework.ai.chat.messages.Message;
 import org.springframework.ai.chat.model.ChatModel;
+import org.springframework.ai.chat.model.ChatResponse;
 import org.springframework.ai.chat.model.ToolContext;
+import org.springframework.ai.model.tool.ToolCallingChatOptions;
 import org.springframework.ai.tool.annotation.Tool;
 import org.springframework.ai.tool.method.MethodToolCallback;
 import org.springframework.ai.tool.support.ToolDefinitions;
@@ -39,6 +44,8 @@
 import org.springframework.test.context.ActiveProfiles;
 import org.springframework.util.ReflectionUtils;
 
+import reactor.core.publisher.Flux;
+
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.AssertionsForClassTypes.assertThatThrownBy;
 
@@ -262,6 +269,39 @@ void toolAnnotation() {
 			.containsEntry("color", TestFunctionClass.LightColor.RED);
 	}
 
+	// https://github.com/spring-projects/spring-ai/issues/1878
+	@ParameterizedTest
+	@ValueSource(strings = { "claude-opus-4-20250514", "claude-sonnet-4-20250514", "claude-3-7-sonnet-latest" })
+	void streamingParameterLessTool(String modelName) {
+
+		ChatClient chatClient = ChatClient.builder(this.chatModel).build();
+
+		Flux<ChatResponse> responses = chatClient.prompt()
+			.options(ToolCallingChatOptions.builder().model(modelName).build())
+			.tools(new ParameterLessTools())
+			.user("Get current weather in Amsterdam")
+			.stream()
+			.chatResponse();
+
+		String content = responses.collectList()
+			.block()
+			.stream()
+			.filter(cr -> cr.getResult() != null)
+			.map(cr -> cr.getResult().getOutput().getText())
+			.collect(Collectors.joining());
+
+		assertThat(content).contains("20 degrees");
+	}
+
+	public static class ParameterLessTools {
+
+		@Tool(description = "Get the current weather forecast in Amsterdam")
+		String getCurrentDateTime() {
+			return "Weather is hot and sunny with a temperature of 20 degrees";
+		}
+
+	}
+
 	@Autowired
 	ChatModel chatModel;