fix build fail issue

idea-plugin/p3c-common/build.gradle

@@ -34,6 +34,8 @@ intellij {
 }
 version '1.0.0'
 
+ext.isReleaseVersion = !version.endsWith("SNAPSHOT")
+
 dependencies {
     compile group: 'org.freemarker', name: 'freemarker', version: '2.3.25-incubating'
     compile 'com.alibaba.p3c:p3c-pmd:1.3.0'
@@ -46,11 +48,11 @@ uploadArchives {
             beforeDeployment { MavenDeployment deployment -> signing.signPom(deployment) }
 
             repository(url: "https://oss.sonatype.org/service/local/staging/deploy/maven2/") {
-                authentication(userName: ossrhUsername, password: ossrhPassword)
+                authentication(userName: findProperty('ossrhUsername'), password: findProperty('ossrhPassword'))
             }
 
             snapshotRepository(url: "https://oss.sonatype.org/content/repositories/snapshots/") {
-                authentication(userName: ossrhUsername, password: ossrhPassword)
+                authentication(userName: findProperty('ossrhUsername'), password: findProperty('ossrhPassword'))
             }
 
             pom.project {
@@ -90,5 +92,8 @@ uploadArchives {
 }
 
 signing {
+    required {
+        isReleaseVersion && gradle.taskGraph.hasTask("uploadArchives")
+    }
     sign configurations.archives
-}
\ No newline at end of file
+}