string concatination

.classpath

@@ -49,6 +49,6 @@
 	<classpathentry exported="true" kind="lib" path="lib/itext-asian-5.2.0.jar"/>
 	<classpathentry exported="true" kind="lib" path="lib/jcommon-1.0.23.jar"/>
 	<classpathentry exported="true" kind="lib" path="lib/jfreechart-1.0.19.jar"/>
-	<classpathentry exported="true" kind="lib" path="lib/google-api-client-1.19.1.jar"/>
+	<classpathentry exported="true" kind="lib" path="lib/google-api-client-1.19.1.jar" sourcepath="lib/src/google-api-client-1.19.1-sources.jar"/>
 	<classpathentry kind="output" path="build/classes"/>
 </classpath>

src/main/java/ilarkesto/core/base/Str.java

@@ -1,14 +1,14 @@
 /*
  * Copyright 2011 Witoslaw Koczewsi <[email protected]>, Artjom Kochtchi
- * 
+ *
  * This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero
  * General Public License as published by the Free Software Foundation, either version 3 of the License, or
  * (at your option) any later version.
- * 
+ *
  * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the
  * implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public
  * License for more details.
- * 
+ *
  * You should have received a copy of the GNU General Public License along with this program. If not, see
  * <http://www.gnu.org/licenses/>.
  */
@@ -435,6 +435,7 @@ public static String concat(Collection strings, String delimiter) {
 		StringBuilder sb = new StringBuilder();
 		boolean first = true;
 		for (Object s : strings) {
+			if (s == null) continue;
 			if (first) {
 				first = false;
 			} else {