Revert "Refactor: Add null check, optimize string joining, and add JavaDocs (spring-projects#3663)"

This reverts commit 8d45caf.

Author: TheEterna

models/spring-ai-openai/src/main/java/org/springframework/ai/openai/api/OpenAiApi.java

@@ -21,7 +21,6 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
-import java.util.stream.Collectors;
 
 import com.fasterxml.jackson.annotation.JsonFormat;
 import com.fasterxml.jackson.annotation.JsonIgnore;
@@ -145,20 +144,11 @@ public OpenAiApi(String baseUrl, ApiKey apiKey, MultiValueMap<String, String> he
 			.build(); // @formatter:on
 	}
 
-	/**
-	 * Returns a string containing all text values from the given media content list. Only
-	 * elements of type "text" are processed and concatenated in order.
-	 * @param content The list of {@link ChatCompletionMessage.MediaContent}
-	 * @return a string containing all text values from "text" type elements
-	 * @throws IllegalArgumentException if content is null
-	 */
 	public static String getTextContent(List<ChatCompletionMessage.MediaContent> content) {
-		Assert.notNull(content, "content cannot be null");
-
 		return content.stream()
 			.filter(c -> "text".equals(c.type()))
 			.map(ChatCompletionMessage.MediaContent::text)
-			.collect(Collectors.joining());
+			.reduce("", (a, b) -> a + b);
 	}
 
 	/**