gistfile1.txt

$ kubectl version
Client Version: version.Info{Major:"1", Minor:"17", GitVersion:"v1.17.2", GitCommit:"59603c6e503c87169aea6106f57b9f242f64df89", GitTreeState:"clean", BuildDate:"2020-01-18T23:30:10Z", GoVersion:"go1.13.5", Compiler:"gc", Platform:"darwin/amd64"}
Server Version: version.Info{Major:"1", Minor:"17", GitVersion:"v1.17.2", GitCommit:"59603c6e503c87169aea6106f57b9f242f64df89", GitTreeState:"clean", BuildDate:"2020-02-07T01:05:17Z", GoVersion:"go1.13.5", Compiler:"gc", Platform:"linux/amd64"}

$ kubectl create configmap env-config --from-literal=log_level=INFO
configmap/env-config created

$ cat <<EOL | kubectl create -f -
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    run: nginx
  name: nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      run: nginx
  template:
    metadata:
      labels:
        run: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        env:
        - name: LOG_LEVEL
          valueFrom:
            configMapKeyRef:
              name: env-config
              key: log_level
EOL

$ kubectl patch deploy nginx --patch "$(cat <<'EOL'
{
  "spec": {
    "template": {
      "spec": {
        "containers": [
          {
            "name": "nginx",
            "env": [
              {
                "name": "LOG_LEVEL",
                "value": "INFO",
                "valueFrom": {
                    "$patch": "delete"
                }
              }
            ]
          }
        ]
      }
    }
  }
}
EOL
)"
The Deployment "nginx" is invalid: spec.template.spec.containers[0].env[0].valueFrom: Invalid value: "": must specify one of: `fieldRef`, `resourceFieldRef`, `configMapKeyRef` or `secretKeyRef`

$ kubectl patch deploy nginx --patch "$(cat <<'EOL'
{
  "spec": {
    "template": {
      "spec": {
        "containers": [
          {
            "name": "nginx",
            "env": [
              {
                "name": "LOG_LEVEL",
                "value": "INFO",
                "valueFrom": null
              }
            ]
          }
        ]
      }
    }
  }
}
EOL
)"
deployment.apps/nginx patched

$ kubectl get deploy nginx -o jsonpath='{.spec.template.spec.containers[*].env}'
[map[name:LOG_LEVEL value:INFO]]