Add clarification on the no-op nature of the metric API. (open-teleme…

…try#829) * Add clarification on the no-op nature of the metric API. * Update specification/metrics/api.md Co-authored-by: Armin Ruech <[email protected]> Co-authored-by: Armin Ruech <[email protected]>
carlosalberto · Aug 19, 2020 · a39343c · a39343c
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diff --git a/specification/metrics/api.md b/specification/metrics/api.md
@@ -89,6 +89,15 @@ logging systems.  For this reason, [OpenTelemetry requires a separation of the
 API from the SDK](../library-guidelines.md#requirements), so that different SDKs
 can be configured at run time.
 
+### Behavior of the API in the absence of an installed SDK
+
+In the absence of an installed Metrics SDK, the Metrics API MUST consist only
+of no-ops. None of the calls on any part of the API can have any side effects
+or do anything meaningful. Meters MUST return no-op implementations of any
+instruments. From a user's perspective, calls to these should be ignored without raising errors
+(i.e., *no* `null` references MUST be returned in languages where accessing these results in errors).
+The API MUST NOT throw exceptions on any calls made to it.
+
 ### Measurements
 
 The term _capture_ is used in this document to describe the action