allow @Tool methods without parameters (e.g. get current date, time, etc)

langchain4j/src/main/java/dev/langchain4j/agent/tool/Tool.java

@@ -10,7 +10,13 @@ import static java.lang.annotation.RetentionPolicy.RUNTIME;
 @Target({METHOD})
 public @interface Tool {
 
+    /**
+     * Name of the tool. If not provided, method name will be used.
+     */
     String name() default "";
 
+    /**
+     * Description of the tool. LLM should understand what this tool is for and when it should be used.
+     */
     String value() default "";
 }

langchain4j/src/main/java/dev/langchain4j/model/openai/OpenAiConverters.java

@@ -88,6 +88,9 @@ class OpenAiConverters {
     }
 
     private static dev.ai4j.openai4j.chat.Parameters toOpenAiParameters(ToolParameters toolParameters) {
+        if (toolParameters == null) {
+            return dev.ai4j.openai4j.chat.Parameters.builder().build();
+        }
         return dev.ai4j.openai4j.chat.Parameters.builder()
                 .properties(toolParameters.properties())
                 .required(toolParameters.required())