integrated changes of #225

Author: wumpz

src/main/java/net/sf/jsqlparser/statement/drop/Drop.java

@@ -77,7 +77,7 @@ public String toString() {
 		String sql = "DROP " + type + " "
            + (ifExists?"IF EXISTS ":"") + name.toString();
 
-		if (parameters != null && parameters.size() > 0) {
+		if (parameters != null && !parameters.isEmpty()) {
 			sql += " " + PlainSelect.getStringList(parameters);
 		}
 

src/main/java/net/sf/jsqlparser/statement/select/Distinct.java

@@ -48,7 +48,7 @@ public void setOnSelectItems(List<SelectItem> list) {
 	public String toString() {
 		String sql = "DISTINCT";
 
-		if (onSelectItems != null && onSelectItems.size() > 0) {
+		if (onSelectItems != null && !onSelectItems.isEmpty()) {
 			sql += " ON (" + PlainSelect.getStringList(onSelectItems) + ")";
 		}