Fix NPE during the concatenation

[asha15]

Purpose

$subject

When [secrets] config defined among the other configs, an NPE occurs during encryption, resulting in the deletion of the subsequent configurations mentioned after [secrets] config. This PR will resolves that issue.

After merging this fix, it will no longer be necessary to add the configuration at the end of the file.

Related issue: #60

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• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? yes/no

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[hwupathum]

The NPE occurs with value. Therfore it needs to be checked for null

if (StringUtils.isNotBlank(value)) {
    line = key.concat(" = \"").concat(value).concat("\"");
}