fix SimpleApiKey Assert Message (#3656)

Auto-cherry-pick to 1.0.x

Fixes #3656

Signed-off-by: jonghoon park <dev@jonghoonpark.com>

Author: dev-jonghoonpark

spring-ai-model/src/main/java/org/springframework/ai/model/SimpleApiKey.java

@@ -31,11 +31,11 @@ public record SimpleApiKey(String value) implements ApiKey {
 
 	/**
 	 * Create a new SimpleApiKey.
-	 * @param value the API key value, must not be null or empty
-	 * @throws IllegalArgumentException if value is null or empty
+	 * @param value the API key value, must not be null
+	 * @throws IllegalArgumentException if value is null
 	 */
 	public SimpleApiKey(String value) {
-		Assert.notNull(value, "API key value must not be null or empty");
+		Assert.notNull(value, "API key value must not be null");
 		this.value = value;
 	}