Join comma if not empty or null

A pure Java 11 solution is:

String message = Stream.of("I", null, "Love", "     ", "You")
                       .filter(Objects::nonNull)
                       .filter(Predicate.not(String::isBlank))
                       .collect(Collectors.joining(" "));
System.out.println(message);

I Love You

If you really need to use array - then instead Stream.of() you can do:

Arrays.stream(new String[] { "I", null, "Love", "     ", "You" })

For Java 8 here is a solution using stream API .Filter null and empty Strings and join with a space between each string

String joined = Stream.of(I, love, , u)
      .filter(s -> s != null && !s.isEmpty())
      .collect(Collectors.joining(" "));

For only null skip guava the best choice:

Joiner.on(" ").skipNulls().join("I", null, "love", null, "u")

In Java 8 you can use Stream:

    List<String> list = Arrays.asList("I", " ", "love", null, "you");
    String message = list.stream().filter(StringUtils::isNotBlank)
                     .collect(Collectors.joining(", "));
    System.out.println("message = " + message);