helm install causes nil pointer
You can try below options to debug this further. 

First verify values.yaml and check the values for serviceAccount (default value is true ) that means the helm chart when deployed will create a service account for the deployment. When you create a pod, if you do not specify a service account, it is automatically assigned the default service account in the given namespace. 

serviceAccount:
  # Specifies whether a service account should be created
  create: true
  # Annotations to add to the service account
  annotations: {}
  # The name of the service account to use.
  # If not set and create is true, a name is generated using the fullname template
  name:


Try to deploy your helm chart with create: false and verify if it solves your issue.

Else remove the file hello-world/templates/serviceaccount.yaml and mark serviceaccount as create: false in value.yaml and pass name as default service account of your deployment try to deploy as below

Note I have removed the serviceaccount.yaml 

~/hello$ tree
.
└── hello-world
    ├── charts
    ├── Chart.yaml
    ├── templates
    │   ├── deployment.yaml
    │   ├── _helpers.tpl
    │   ├── ingress.yaml
    │   ├── NOTES.txt
    │   ├── service.yaml
    │   └── tests
    │       └── test-connection.yaml
    └── values.yaml

4 directories, 8 files


set create field as false under values.yaml

$ cat hello-world/values.yaml | grep -i serviceaccount -A 10

serviceAccount:
  # Specifies whether a service account should be created
  create: false
  # Annotations to add to the service account
  annotations: {}
  # The name of the service account to use.
  # If not set and create is true, a name is generated using the fullname template
  name: default


You can fetch your list of serviceaccounts available as below

$ kubectl get serviceaccounts
NAME      SECRETS   AGE
default   1         2d4h


Once deployed helm list will show the namespace used to deploy your chart and serviceaccount from the name space is used for deploeyemnt

$ helm list
NAME                    NAMESPACE       REVISION        UPDATED                                 STATUS          CHART               APP VERSION
hello-world-1580665905  default         1               2020-02-02 17:51:45.631330487 +0000 UTC deployed        hello-world-0.1.0   1.16.0


Get chart details and values post deploeyemtn as below 

$ helm show chart hello-world
apiVersion: v2
appVersion: 1.16.0
description: A Helm chart for Kubernetes
name: hello-world
type: application
version: 0.1.0

$ helm show values hello-world | grep -i serviceaccount -A 10
serviceAccount:
  # Specifies whether a service account should be created
  create: false
  # Annotations to add to the service account
  annotations: {}
  # The name of the service account to use.
  # If not set and create is true, a name is generated using the fullname template
  name: default

podSecurityContext: {}
  # fsGroup: 2000


Get deployed resources as below 

$ kubectl get all -o wide
NAME                                          READY   STATUS    RESTARTS   AGE    IP               NODE         NOMINATED NODE   READINESS GATES
pod/hello-world-1580665905-84b9d4d469-xv5mx   1/1     Running   0          118s   192.168.58.215   k8s-node02   &lt;none&gt;           &lt;none&gt;

NAME                             TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE    SELECTOR
service/hello-world-1580665905   ClusterIP   10.108.73.21   &lt;none&gt;        80/TCP    118s   app.kubernetes.io/instance=hello-world-1580665905,app.kubernetes.io/name=hello-world
service/kubernetes               ClusterIP   10.96.0.1      &lt;none&gt;        443/TCP   2d4h   &lt;none&gt;

NAME                                     READY   UP-TO-DATE   AVAILABLE   AGE    CONTAINERS    IMAGES         SELECTOR
deployment.apps/hello-world-1580665905   1/1     1            1           118s   hello-world   nginx:1.16.0   app.kubernetes.io/instance=hello-world-1580665905,app.kubernetes.io/name=hello-world

NAME                                                DESIRED   CURRENT   READY   AGE    CONTAINERS    IMAGES         SELECTOR
replicaset.apps/hello-world-1580665905-84b9d4d469   1         1         1       118s   hello-world   nginx:1.16.0   app.kubernetes.io/instance=hello-world-1580665905,app.kubernetes.io/name=hello-world,pod-template-hash=84b9d4d469