code: static JbcSrcJavaValue ofConstantNull(JbcSrcValueErrorReporter reporter) {
      return new JbcSrcJavaValue(
          SoyExpression.NULL,
          /* method= */ null,
          /* allowedType= */ null,
          /* constantNull= */ true,
          /* error= */ false,
          reporter);
    }
docs: Constructs a JbcSrcJavaValue specifically for 'constantNull', in which case the 'allowedType'
  is any valid type (including specific proto or proto enum types). There's no SoyType we can use
  to indicate this, and we can't construct our own SoyType because the cxtor is package-private,
  so we have a separate bool to indicate it.