Only fetch publishing information when relevant envvars are set

lib/build.gradle

@@ -44,14 +44,19 @@ tasks.named('test') {
     useJUnitPlatform()
 }
 
+String repository_url = System.getenv("REPOSITORY_URL")
+String username = System.getenv("USERNAME")
+String password = System.getenv("TOKEN")
+if (repository_url && username && password) {
+
     publishing {
         repositories {
             maven {
                 name = "OSSRH"
-            url = uri(System.getenv("REPOSITORY_URL"))
+                url = uri(repository_url)
                 credentials {
-                username = System.getenv("USERNAME")
-                password = System.getenv("TOKEN")
+                    username = username
+                    password = password
                 }
             }
         }
@@ -63,3 +68,5 @@ publishing {
             }
         }
     }
+
+}