Added ability to disable base_url in Helm chart (#3619)

diff --git a/deploy/kubernetes/helm/templates/tools.yaml b/deploy/kubernetes/helm/templates/tools.yaml
index 7632485..d63beed 100644
--- a/deploy/kubernetes/helm/templates/tools.yaml
+++ b/deploy/kubernetes/helm/templates/tools.yaml
@@ -116,7 +116,9 @@
             - >-
               heron-ui
               --port=8889
-              --base_url={{ .Values.heron.url | default $defaultUrl }}
+              {{- if not (kindIs "invalid" .Values.heron.url) }}
+              --base_url={{ eq .Values.heron.url "-" | ternary $defaultUrl .Values.heron.url }}
+              {{- end }}
         - name: heron-apiserver
           image: {{ .Values.image }}
           imagePullPolicy: {{ .Values.imagePullPolicy }}
diff --git a/deploy/kubernetes/helm/values.yaml.template b/deploy/kubernetes/helm/values.yaml.template
index 5c25b81..8abf328 100644
--- a/deploy/kubernetes/helm/values.yaml.template
+++ b/deploy/kubernetes/helm/values.yaml.template
@@ -39,7 +39,9 @@
 # amount of memory to provide for API server
 apiServerMemory: 512M
 heron:
-  url: ~
+  # set to `-` to set base_url to the default k8s proxy URL
+  # set to `null` to remove the use of base_url
+  url: "-"
 # Topologies uploader
 uploader:
   class: dlog # s3