Add errorprone checking.

And a fix to the signing requirements error.

Author: Capstan

build.gradle

@@ -17,12 +17,17 @@
  * - ASL 2.0: http://www.apache.org/licenses/LICENSE-2.0.txt
  */
 
+plugins {
+    id("net.ltgt.errorprone") version "0.8.1" apply false
+}
+
 apply(plugin: "java");
 apply(plugin: "maven");
 apply(plugin: "signing");
 apply(plugin: "osgi");
 apply(plugin: "idea");
 apply(plugin: "eclipse");
+apply(plugin: "net.ltgt.errorprone");
 
 apply(from: "project.gradle");
 
@@ -35,6 +40,14 @@ repositories {
     mavenCentral();
 }
 
+/*
+ * Add errorprone checking.
+ */
+dependencies {
+    errorprone("com.google.errorprone:error_prone_core:2.3.3")
+    errorproneJavac("com.google.errorprone:javac:9+181-r4173-1")
+}
+
 /*
  * Necessary! Otherwise TestNG will not be used...
  *
@@ -116,7 +129,7 @@ task checkSigningRequirements {
         requiredProperties.each {
             if (project.properties[it] == null) {
                 noDice = true;
-                System.err.printf("property \"%s\" is not defined!")
+                System.err.printf("property \"%s\" is not defined!\n")
             }
         }
         if (noDice)