Guard version env defaults in pipeline

Jenkinsfile

@@ -64,8 +64,8 @@ spec:
     REGISTRY = 'registry.bstein.dev/bstein'
     FRONT_IMAGE = "${REGISTRY}/bstein-dev-home-frontend"
     BACK_IMAGE  = "${REGISTRY}/bstein-dev-home-backend"
-    VERSION_TAG = ''
-    SEMVER = ''
+    VERSION_TAG = 'dev'
+    SEMVER = 'dev'
   }
   options {
     disableConcurrentBuilds()
@@ -113,7 +113,7 @@ spec:
               echo "SEMVER=${SEMVER}" > build.env
             '''
             def props = readProperties file: 'build.env'
-            env.SEMVER = props['SEMVER']
+            env.SEMVER = props['SEMVER'] ?: "0.1.0-${env.BUILD_NUMBER}"
             env.VERSION_TAG = env.SEMVER
           }
         }