Merge pull request #35 from marcusholl/pr/FixDefaultValueCacheGetInstance

fix default value cache get instance

src/com/sap/piper/DefaultValueCache.groovy

@@ -1,5 +1,7 @@
 package com.sap.piper
 
+import com.cloudbees.groovy.cps.NonCPS
+
 class DefaultValueCache implements Serializable {
     private static DefaultValueCache instance
 
@@ -9,6 +11,7 @@ class DefaultValueCache implements Serializable {
         this.defaultValues = defaultValues
     }
 
+    @NonCPS
     static getInstance(){
         return instance
     }
@@ -17,6 +20,7 @@ class DefaultValueCache implements Serializable {
         instance = new DefaultValueCache(defaultValues)
     }
 
+    @NonCPS
     Map getDefaultValues(){
         return defaultValues
     }