Fix preconditions errors (added guava)

Author: njb-said

pom.xml

@@ -24,6 +24,12 @@
             <artifactId>jcabi-aspects</artifactId>
             <version>1.0-SNAPSHOT</version>
         </dependency>
+        
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>18.0</version>
+        </dependency>
     </dependencies>
 
     <build>