Beautified code and added Normalized word functionality on OneWords

src/main/java/alg/XML_processing.java

@@ -892,7 +892,7 @@ public class XML_processing {
 		if (filter.getAl() == AnalysisLevel.STRING_LEVEL) {
 			// ngram level: if not 0 must be less than or equal to number of words in this sentence.
 			if (filter.getNgramValue() > 0 && filter.getNgramValue() > sentence.size()) {
-				return null;
+				return new ArrayList<>();
 			}
 
 			// if we're calculating values for letters, omit words that are shorter than string length