Protect against empty OS string in Docker Image

Update `Image` to protect against `os` being `null` or and empty
String.

Fixes gh-45152

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/main/java/org/springframework/boot/buildpack/platform/docker/type/Image.java

@@ -26,6 +26,7 @@ import java.util.List;
 import com.fasterxml.jackson.databind.JsonNode;
 
 import org.springframework.boot.buildpack.platform.json.MappedObject;
+import org.springframework.util.StringUtils;
 
 /**
  * Image details as returned from {@code Docker inspect}.
@@ -90,7 +91,7 @@ public class Image extends MappedObject {
 	 * @return the image OS
 	 */
 	public String getOs() {
-		return (this.os != null) ? this.os : "linux";
+		return (!StringUtils.hasText(this.os)) ? this.os : "linux";
 	}
 
 	/**