Fix config handling with empty config entries after merge

Fixes #8701

common/maps/params.go

@@ -52,6 +52,24 @@ func (p Params) Set(pp Params) {
 	}
 }
 
+// IsZero returns true if p is considered empty.
+func (p Params) IsZero() bool {
+	if p == nil || len(p) == 0 {
+		return true
+	}
+
+	if len(p) > 1 {
+		return false
+	}
+
+	for k, _ := range p {
+		return k == mergeStrategyKey
+	}
+
+	return false
+
+}
+
 // Merge transfers values from pp to p for new keys.
 // This is done recursively.
 func (p Params) Merge(pp Params) {
@@ -82,12 +100,9 @@ func (p Params) merge(ps ParamsMergeStrategy, pp Params) {
 				if pv, ok := v.(Params); ok {
 					vvv.merge(ms, pv)
 				}
-
 			}
-
 		} else if !noUpdate {
 			p[k] = v
-
 		}
 
 	}

common/maps/params_test.go

@@ -156,3 +156,15 @@ func TestParamsSetAndMerge(t *testing.T) {
 	})
 
 }
+
+func TestParamsIsZero(t *testing.T) {
+	c := qt.New(t)
+
+	var nilParams Params
+
+	c.Assert(Params{}.IsZero(), qt.IsTrue)
+	c.Assert(nilParams.IsZero(), qt.IsTrue)
+	c.Assert(Params{"foo": "bar"}.IsZero(), qt.IsFalse)
+	c.Assert(Params{"_merge": "foo", "foo": "bar"}.IsZero(), qt.IsFalse)
+	c.Assert(Params{"_merge": "foo"}.IsZero(), qt.IsTrue)
+}