Use Collections.isEmpty() instead of .size() == 0

Ensure that Collections.isEmpty() is used to check if there are no
elements in a collections. This is more explicit and can be faster than
calling .size().

Closes gh-4783

spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/PropertiesMergingResourceTransformer.java

@@ -73,7 +73,7 @@ public class PropertiesMergingResourceTransformer implements ResourceTransformer
 
 	@Override
 	public boolean hasTransformedResource() {
-		return this.data.size() > 0;
+		return !this.data.isEmpty();
 	}
 
 	@Override