private String getSingleStringValue(List<String> values) {

        String value = getSingleValue(values);
        if (value != null && !value.isEmpty())
            return value;

        return null;

    }
Returns the single value stored in the given list of strings. If the
list is empty, contains multiple values, or contains only a single empty
string, null is returned. Note that null will also be returned if the
single value stored in the list is itself null.

@param values
    The list to retrieve a single value from.

@return
    The single value stored in the given list, or null if the list is
    empty, contains multiple values, or contains only a single empty
    string.
extensions/guacamole-vault/modules/guacamole-vault-ksm/src/main/java/org/apache/guacamole/vault/ksm/secret/KsmRecordService.java