Fix defaulting a component with empty value (#3690)

Signed-off-by: Pavol Loffay <[email protected]>

Author: pavolloffay

.chloggen/3452.yaml

@@ -0,0 +1,22 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. collector, target allocator, auto-instrumentation, opamp, github action)
+component: collector
+
+# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix config handling with null values.
+
+# One or more tracking issues related to the change
+issues: [3452]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: |
+  Fix the defaulting webhook error `src and dst must not be nil` caused by defaulting a known component with a null value:
+  e.g. 
+  ```yaml
+  receivers:
+    zipkin:
+  ```

apis/v1beta1/config.go

@@ -306,6 +306,9 @@ func (c *Config) applyDefaultForComponentKinds(logger logr.Logger, componentKind
 				continue
 			}
 
+			if componentConf == nil {
+				componentConf = map[string]interface{}{}
+			}
 			if err := mergo.Merge(&mappedCfg, componentConf); err != nil {
 				return err
 			}

apis/v1beta1/config_test.go

@@ -77,6 +77,22 @@ func TestNullObjects(t *testing.T) {
 	assert.Equal(t, []string{"connectors.spanmetrics:", "exporters.otlp.endpoint:", "extensions.health_check:", "processors.batch:", "receivers.otlp.protocols.grpc:", "receivers.otlp.protocols.http:"}, nullObjects)
 }
 
+func TestNullObjects_issue_3445(t *testing.T) {
+	collectorYaml, err := os.ReadFile("./testdata/issue-3452.yaml")
+	require.NoError(t, err)
+
+	collectorJson, err := yaml.YAMLToJSON(collectorYaml)
+	require.NoError(t, err)
+
+	cfg := &Config{}
+	err = json.Unmarshal(collectorJson, cfg)
+	require.NoError(t, err)
+
+	err = cfg.ApplyDefaults(logr.Discard())
+	require.NoError(t, err)
+	assert.Empty(t, cfg.nullObjects())
+}
+
 func TestConfigFiles_go_yaml(t *testing.T) {
 	files, err := os.ReadDir("./testdata")
 	require.NoError(t, err)

apis/v1beta1/testdata/issue-3452.yaml

@@ -0,0 +1,6 @@
+receivers:
+  zipkin:
+service:
+  pipelines:
+    traces:
+      receivers: [zipkin]