Fix docker build

build.gradle

@@ -172,8 +172,8 @@ jib {
             add project.version.toString().replaceAll('(\\d+\\.\\d+).+', '$1')
         }
         auth {
-            username = System.getenv('DOCKERHUB_USERNAME')
-            password = System.getenv('DOCKERHUB_TOKEN')
+            username = System.getenv('DOCKERHUB_USERNAME') ?: ''
+            password = System.getenv('DOCKERHUB_TOKEN') ?: ''
         }
     }
     container {

gradle/libs.versions.toml

@@ -136,7 +136,7 @@ junit = ["junit-jupiter", "assertj"]
 
 [plugins]
 kotlin = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
-jib = { id = "com.google.cloud.tools.jib", version = "2.5.0" }
+jib = { id = "com.google.cloud.tools.jib", version = "2.7.1" }
 spring = { id = "org.springframework.boot", version = "2.6.0" }
 git = { id = "com.palantir.git-version", version = "0.12.3" }
 protobuf = { id = "com.google.protobuf", version = "0.9.1" }