[PORT]Ignore the null or empty result of the OutputFormat in TextInput

[Danieladu]

Original issue: https://github.com/microsoft/botbuilder-dotnet/issues/4758
Original PR: microsoft/botbuilder-dotnet#4814

Description

If someone assigns an empty string or null value or whitespace string to property OutputFormat, would trigger the unrecognized prompt error.

Specific Changes

Ignore the null or whitespace string in OutputFormat.

Testing

Such action:

{
           "$kind": "Microsoft.TextInput",
           "property": "user.name",
           "alwaysPrompt": true,
           "prompt": "Hello, what is your name?",
            "unrecognizedPrompt": "How should I call you?",
            "validations": [
                   "this.value.Length > 3"
             ],
             "outputFormat": "" // would ignore this property
 }

[joshgummersall]

One quick suggestion.

[joshgummersall]

It seems strange to call toString() after calling trim() which implies value is a string. Also, do we want to assign the trimmed string to input? Maybe this should be:

const maybeValue = this.outputFormat.getValue(dc.state);
if (maybeValue && typeof maybeValue === 'string') {
  const value = maybeValue.trim();
  if (value) {
    input = value;
  }
}

[Danieladu]

Yes. The original toString() seems redundant because the return type of this.outputFormat.getValue(dc.state) is string | undefined, so, just remove the toString() is ok?