2 files changed, 32 insertions, 9 deletions

diff --git a/Jenkinsfile b/Jenkinsfile
index f7f3f28..3b197f4 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -10,19 +10,40 @@ pipeline {
             steps {
                 script {
                     def base = env.CHANGE_TARGET ? "origin/${env.CHANGE_TARGET}" : "HEAD~1"
-                    def changed = sh(
-                        script: "git diff --name-only ${base} HEAD | cut -d/ -f1 | sort -u",
+
+                    // returnStdout gives a String. Trim, split, and FORCE to a List.
+                    def diffOutput = sh(
+                        script: "git diff --name-only ${base} HEAD || true",
                         returnStdout: true
-                    ).trim().split('\n')
+                    ).trim()
+
+                    // 'as List' avoids the non-serializable String[] array
+                    def changedFiles = diffOutput ? (diffOutput.split('\n') as List) : []
+
+                    // Build a plain List of unique top-level dirs (Strings only)
+                    def candidates = []
+                    for (String f : changedFiles) {
+                        def top = f.split('/')[0]
+                        if (top && !candidates.contains(top)) {
+                            candidates.add(top)
+                        }
+                    }
 
-                    // keep only dirs containing a Dockerfile
-                    env.IMAGES_TO_BUILD = changed.findAll {
-                        fileExists("${it}/Dockerfile")
-                    }.join(',')
+                    // fileExists is a pipeline STEP, so it must stay in CPS land
+                    // (i.e. a normal for-loop, NOT inside @NonCPS or a findAll closure)
+                    def toBuild = []
+                    for (String dir : candidates) {
+                        if (fileExists("${dir}/Dockerfile")) {
+                            toBuild.add(dir)
+                        }
+                    }
+
+                    // Store only a plain String in env
+                    env.IMAGES_TO_BUILD = toBuild.join(',')
+                    echo "Images to build: ${env.IMAGES_TO_BUILD ?: '(none)'}"
                 }
             }
         }
-
         stage('Build & push') {
             when { expression { env.IMAGES_TO_BUILD } }
             steps {
@@ -49,4 +70,4 @@ pipeline {
             }
         }
     }
-}
\ No newline at end of file
+}
diff --git a/test-1/Dockerfile b/test-1/Dockerfile
index b4e1dd4..f32e3e8 100644
--- a/test-1/Dockerfile
+++ b/test-1/Dockerfile
@@ -2,4 +2,6 @@ FROM ubuntu:latest
 
 RUN apt update && apt install -y git
 
+RUN git --version
+
 ENTRYPOINT ['git']