fix: keep nil map values in EqualExportedValues

assert/assertions.go

@@ -136,6 +136,15 @@ func copyExportedFields(expected interface{}) interface{} {
 		for _, k := range expectedValue.MapKeys() {
 			index := expectedValue.MapIndex(k)
 			unexportedRemoved := copyExportedFields(index.Interface())
+			if unexportedRemoved == nil {
+				// reflect.ValueOf(nil) is the zero Value, which
+				// SetMapIndex interprets as "delete this key". Store the
+				// element type's zero value instead so nil map values are
+				// preserved and the entry keeps taking part in the
+				// comparison.
+				result.SetMapIndex(k, reflect.Zero(expectedType.Elem()))
+				continue
+			}
 			result.SetMapIndex(k, reflect.ValueOf(unexportedRemoved))
 		}
 		return result.Interface()

assert/assertions_test.go

@@ -508,6 +508,29 @@ func TestEqualExportedValues(t *testing.T) {
 	            	+  Exported: (int) 2,
 	            	   notExported: (interface {}) <nil>`,
 		},
+		// A map entry holding a nil interface value is still an entry: the
+		// key must not be dropped while copying, otherwise maps with
+		// different keys would wrongly compare as equal.
+		{
+			value1:        map[string]interface{}{"a": nil},
+			value2:        map[string]interface{}{"a": nil},
+			expectedEqual: true,
+		},
+		{
+			value1:        map[string]interface{}{"a": nil},
+			value2:        map[string]interface{}{},
+			expectedEqual: false,
+		},
+		{
+			value1:        map[string]interface{}{"a": nil, "b": 1},
+			value2:        map[string]interface{}{"b": 1},
+			expectedEqual: false,
+		},
+		{
+			value1:        map[string]interface{}{"a": nil},
+			value2:        map[string]interface{}{"a": 1},
+			expectedEqual: false,
+		},
 	}
 
 	for _, c := range cases {