Empty string should be a valid attribute value

[trask]

From https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/common/README.md#attribute:

Attribute values expressing a numerical value of zero, an empty string, or an empty array are considered meaningful and MUST be stored and passed on to processors / exporters.

Empty strings are important for url.query where empty strings are important to preserve to represent urls like http://xyz/path?

The Span API javadoc currently says that the behavior for an empty string value is "undefined" (I haven't checked what the actual implementation does):

opentelemetry-java/api/all/src/main/java/io/opentelemetry/api/trace/Span.java

Lines 94 to 95 in 60bb0a7

	* <p>If a null or empty String {@code value} is passed in, the behavior is undefined, and hence
	* strongly discouraged.

[jack-berg]

It looks like the implementation ignores null values, but sets empty strings. Should update the javadoc and confirm with a test (if none exists) while we're at it.

[erharjotsingh]

/assign erharjotsingh

[erharjotsingh]

hello @jack-berg @trask
Could you please summarize the issue and give me some pointers. Please assign to me and I can pick this up. Thanks!

[breedx-splk]

It looks like the implementation ignores null values, but sets empty strings. Should update the javadoc and confirm with a test (if none exists) while we're at it.

There are tests that covers it for the SdkSpan:

• https://github.com/open-telemetry/opentelemetry-java/blob/main/sdk/trace/src/test/java/io/opentelemetry/sdk/trace/SdkSpanTest.java#L434
• https://github.com/open-telemetry/opentelemetry-java/blob/main/sdk/trace/src/test/java/io/opentelemetry/sdk/trace/SdkSpanTest.java#L506