[otlp-exporters] passing an undefined header values crashes end-user apps

[pichlermarc]

What happened?

When passing an options object like { headers: { foo: undefined } } to the http/json and http/protobuf exporters, the headers will not be validated and that will cause

opentelemetry-js/experimental/packages/otlp-exporter-base/src/platform/node/util.ts

Line 89 in abfe059

req = request(options, (res: http.IncomingMessage) => {

to throw, as we're passing an undefined header value. While this alone will not cause an application crash, trying to access req at

opentelemetry-js/experimental/packages/otlp-exporter-base/src/platform/node/util.ts

Line 62 in abfe059

if (req.destroyed) {

will cause the end-user's application to crash within typically 10s after the first export (when using defaults).