Check for empty string

Signed-off-by: Arthit Suriyawongkul <[email protected]>

Author: bact

src/main/java/org/spdx/utility/compare/LicenseCompareHelper.java

@@ -94,7 +94,7 @@ public static String licenseUriToLicenseId(String objectUri) {
 	 * @return string without comment characters
 	 */
 	public static String removeCommentChars(String s) {
-		if (s == null) {
+		if (s == null || s.isEmpty()) {
 			return "";
 		}
 		StringBuilder sb = new StringBuilder();