tags.go.tpl file in code-generator doesn't handle some edge cases

[kyriechen96]

Describe the bug
By using v0.20.1 version of code generator to generate controller, the function of ToACKTags cannot handle edge case of tag that both key and value are nil.

Steps to reproduce
applying yaml file:

apiVersion: memorydb.services.k8s.aws/v1alpha1
kind: ParameterGroup
metadata:
  name: test
spec:
    description: test
    family: memorydb_redis6
    name: test
    parameterNameValues:
          - parameterName: activerehashing
            parameterValue: "no"
    tags:
     - key: "1"
       value: "1"
     - key: 

Expected outcome
Controller works well.

Outcome
Controller stops running after applying a tag with nil key and nil value.

[a-hilaly]

Fixed in aws-controllers-k8s/code-generator#374