NIFI-8943 Corrected Sensitive Props Key handling in Docker

Signed-off-by: Pierre Villard <pierre.villard.fr@gmail.com>

This closes #5245.
diff --git a/nifi-docker/dockerhub/sh/start.sh b/nifi-docker/dockerhub/sh/start.sh
index 9cce534..c67c6f1 100755
--- a/nifi-docker/dockerhub/sh/start.sh
+++ b/nifi-docker/dockerhub/sh/start.sh
@@ -98,7 +98,9 @@
 prop_replace 'nifi.analytics.connection.model.score.name'       "${NIFI_ANALYTICS_MODEL_SCORE_NAME:-rSquared}"
 prop_replace 'nifi.analytics.connection.model.score.threshold'  "${NIFI_ANALYTICS_MODEL_SCORE_THRESHOLD:-.90}"
 
-prop_replace 'nifi.sensitive.props.key'   "${NIFI_SENSITIVE_PROPS_KEY:-}"
+if [ -n "${NIFI_SENSITIVE_PROPS_KEY}" ]; then
+    prop_replace 'nifi.sensitive.props.key' "${NIFI_SENSITIVE_PROPS_KEY}"
+fi
 
 if [ -n "${SINGLE_USER_CREDENTIALS_USERNAME}" ] && [ -n "${SINGLE_USER_CREDENTIALS_PASSWORD}" ]; then
     ${NIFI_HOME}/bin/nifi.sh set-single-user-credentials "${SINGLE_USER_CREDENTIALS_USERNAME}" "${SINGLE_USER_CREDENTIALS_PASSWORD}"
diff --git a/nifi-docker/dockermaven/sh/start.sh b/nifi-docker/dockermaven/sh/start.sh
index ce27142..3b251b5 100755
--- a/nifi-docker/dockermaven/sh/start.sh
+++ b/nifi-docker/dockermaven/sh/start.sh
@@ -98,7 +98,9 @@
 prop_replace 'nifi.analytics.connection.model.score.name'       "${NIFI_ANALYTICS_MODEL_SCORE_NAME:-rSquared}"
 prop_replace 'nifi.analytics.connection.model.score.threshold'  "${NIFI_ANALYTICS_MODEL_SCORE_THRESHOLD:-.90}"
 
-prop_replace 'nifi.sensitive.props.key'   "${NIFI_SENSITIVE_PROPS_KEY:-}"
+if [ -n "${NIFI_SENSITIVE_PROPS_KEY}" ]; then
+    prop_replace 'nifi.sensitive.props.key' "${NIFI_SENSITIVE_PROPS_KEY}"
+fi
 
 if [ -n "${SINGLE_USER_CREDENTIALS_USERNAME}" ] && [ -n "${SINGLE_USER_CREDENTIALS_PASSWORD}" ]; then
     ${NIFI_HOME}/bin/nifi.sh set-single-user-credentials "${SINGLE_USER_CREDENTIALS_USERNAME}" "${SINGLE_USER_CREDENTIALS_PASSWORD}"