diff --git a/coverage_test.go b/coverage_test.go
new file mode 100644
index 0000000..ea39817
--- /dev/null
+++ b/coverage_test.go
@@ -0,0 +1,568 @@
+package json
+
+import (
+	"bytes"
+	"fmt"
+	"strings"
+	"testing"
+)
+
+func intptr(v int) *int {
+	return &v
+}
+
+func int8ptr(v int8) *int8 {
+	return &v
+}
+
+func headIntPtrNilNotRoot() interface{} {
+	v := struct {
+		A struct {
+			A *int `json:"a"`
+		}
+	}{}
+	return v
+}
+
+func ptrHeadIntNotRoot() interface{} {
+	v := struct {
+		A *struct {
+			A int `json:"a"`
+		}
+	}{A: new(struct {
+		A int `json:"a"`
+	})}
+	v.A.A = 1
+	return v
+}
+
+func TestCoverage(t *testing.T) {
+	tests := []struct {
+		name     string
+		expected string
+		data     interface{}
+	}{
+		{
+			name:     "HeadIntZero",
+			expected: `{"a":0}`,
+			data: struct {
+				A int `json:"a"`
+			}{},
+		},
+		{
+			name:     "HeadInt",
+			expected: `{"a":1}`,
+			data: struct {
+				A int `json:"a"`
+			}{A: 1},
+		},
+		{
+			name:     "HeadIntPtr",
+			expected: `{"a":1}`,
+			data: struct {
+				A *int `json:"a"`
+			}{A: intptr(1)},
+		},
+		{
+			name:     "HeadIntPtrNil",
+			expected: `{"a":null}`,
+			data: struct {
+				A *int `json:"a"`
+			}{A: nil},
+		},
+		{
+			name:     "PtrHeadIntZero",
+			expected: `{"a":0}`,
+			data: &struct {
+				A int `json:"a"`
+			}{},
+		},
+		{
+			name:     "PtrHeadInt",
+			expected: `{"a":1}`,
+			data: &struct {
+				A int `json:"a"`
+			}{A: 1},
+		},
+		{
+			name:     "PtrHeadIntPtr",
+			expected: `{"a":1}`,
+			data: &struct {
+				A *int `json:"a"`
+			}{A: intptr(1)},
+		},
+		{
+			name:     "PtrHeadIntPtrNil",
+			expected: `{"a":null}`,
+			data: &struct {
+				A *int `json:"a"`
+			}{A: nil},
+		},
+		{
+			name:     "PtrHeadIntNil",
+			expected: `null`,
+			data: (*struct {
+				A *int `json:"a"`
+			})(nil),
+		},
+		{
+			name:     "HeadIntZeroMultiFields",
+			expected: `{"a":0,"b":0}`,
+			data: struct {
+				A int `json:"a"`
+				B int `json:"b"`
+			}{},
+		},
+		{
+			name:     "HeadIntMultiFields",
+			expected: `{"a":1,"b":2}`,
+			data: struct {
+				A int `json:"a"`
+				B int `json:"b"`
+			}{A: 1, B: 2},
+		},
+		{
+			name:     "HeadIntPtrMultiFields",
+			expected: `{"a":1,"b":2}`,
+			data: struct {
+				A *int `json:"a"`
+				B *int `json:"b"`
+			}{A: intptr(1), B: intptr(2)},
+		},
+		{
+			name:     "HeadIntPtrNilMultiFields",
+			expected: `{"a":null,"b":null}`,
+			data: struct {
+				A *int `json:"a"`
+				B *int `json:"b"`
+			}{A: nil, B: nil},
+		},
+		{
+			name:     "PtrHeadIntZeroMultiFields",
+			expected: `{"a":0,"b":0}`,
+			data: &struct {
+				A int `json:"a"`
+				B int `json:"b"`
+			}{},
+		},
+		{
+			name:     "PtrHeadIntMultiFields",
+			expected: `{"a":1,"b":2}`,
+			data: &struct {
+				A int `json:"a"`
+				B int `json:"b"`
+			}{A: 1, B: 2},
+		},
+		{
+			name:     "PtrHeadIntPtrMultiFields",
+			expected: `{"a":1,"b":2}`,
+			data: &struct {
+				A *int `json:"a"`
+				B *int `json:"b"`
+			}{A: intptr(1), B: intptr(2)},
+		},
+		{
+			name:     "PtrHeadIntPtrNilMultiFields",
+			expected: `{"a":null,"b":null}`,
+			data: &struct {
+				A *int `json:"a"`
+				B *int `json:"b"`
+			}{A: nil, B: nil},
+		},
+		{
+			name:     "PtrHeadIntNilMultiFields",
+			expected: `null`,
+			data: (*struct {
+				A *int `json:"a"`
+				B *int `json:"b"`
+			})(nil),
+		},
+
+		{
+			name:     "HeadIntZeroNotRoot",
+			expected: `{"A":{"a":0}}`,
+			data: struct {
+				A struct {
+					A int `json:"a"`
+				}
+			}{},
+		},
+		{
+			name:     "HeadIntNotRoot",
+			expected: `{"A":{"a":1}}`,
+			data: struct {
+				A struct {
+					A int `json:"a"`
+				}
+			}{A: struct {
+				A int `json:"a"`
+			}{A: 1}},
+		},
+		{
+			name:     "HeadIntPtrNotRoot",
+			expected: `{"A":{"a":1}}`,
+			data: struct {
+				A struct {
+					A *int `json:"a"`
+				}
+			}{A: struct {
+				A *int `json:"a"`
+			}{intptr(1)}},
+		},
+		{
+			name:     "HeadIntPtrNilNotRoot",
+			expected: `{"A":{"a":null}}`,
+			data: struct {
+				A struct {
+					A *int `json:"a"`
+				}
+			}{},
+		},
+		{
+			name:     "PtrHeadIntZeroNotRoot",
+			expected: `{"A":{"a":0}}`,
+			data: struct {
+				A *struct {
+					A int `json:"a"`
+				}
+			}{A: new(struct {
+				A int `json:"a"`
+			})},
+		},
+		{
+			name:     "PtrHeadIntNotRoot",
+			expected: `{"A":{"a":1}}`,
+			data: struct {
+				A *struct {
+					A int `json:"a"`
+				}
+			}{A: &(struct {
+				A int `json:"a"`
+			}{A: 1})},
+		},
+		{
+			name:     "PtrHeadIntPtrNotRoot",
+			expected: `{"A":{"a":1}}`,
+			data: struct {
+				A *struct {
+					A *int `json:"a"`
+				}
+			}{A: &(struct {
+				A *int `json:"a"`
+			}{A: intptr(1)})},
+		},
+		{
+			name:     "PtrHeadIntPtrNilNotRoot",
+			expected: `{"A":{"a":null}}`,
+			data: struct {
+				A *struct {
+					A *int `json:"a"`
+				}
+			}{A: &(struct {
+				A *int `json:"a"`
+			}{A: nil})},
+		},
+		{
+			name:     "PtrHeadIntNilNotRoot",
+			expected: `{"A":null}`,
+			data: struct {
+				A *struct {
+					A *int `json:"a"`
+				}
+			}{A: nil},
+		},
+		{
+			name:     "HeadIntZeroMultiFieldsNotRoot",
+			expected: `{"A":{"a":0},"B":{"b":0}}`,
+			data: struct {
+				A struct {
+					A int `json:"a"`
+				}
+				B struct {
+					B int `json:"b"`
+				}
+			}{},
+		},
+		{
+			name:     "HeadIntMultiFieldsNotRoot",
+			expected: `{"A":{"a":1},"B":{"b":2}}`,
+			data: struct {
+				A struct {
+					A int `json:"a"`
+				}
+				B struct {
+					B int `json:"b"`
+				}
+			}{A: struct {
+				A int `json:"a"`
+			}{A: 1}, B: struct {
+				B int `json:"b"`
+			}{B: 2}},
+		},
+		{
+			name:     "HeadIntPtrMultiFieldsNotRoot",
+			expected: `{"A":{"a":1},"B":{"b":2}}`,
+			data: struct {
+				A struct {
+					A *int `json:"a"`
+				}
+				B struct {
+					B *int `json:"b"`
+				}
+			}{A: struct {
+				A *int `json:"a"`
+			}{A: intptr(1)}, B: struct {
+				B *int `json:"b"`
+			}{B: intptr(2)}},
+		},
+		{
+			name:     "HeadIntPtrNilMultiFieldsNotRoot",
+			expected: `{"A":{"a":null},"B":{"b":null}}`,
+			data: struct {
+				A struct {
+					A *int `json:"a"`
+				}
+				B struct {
+					B *int `json:"b"`
+				}
+			}{A: struct {
+				A *int `json:"a"`
+			}{A: nil}, B: struct {
+				B *int `json:"b"`
+			}{B: nil}},
+		},
+		{
+			name:     "PtrHeadIntZeroMultiFieldsNotRoot",
+			expected: `{"A":{"a":0},"B":{"b":0}}`,
+			data: &struct {
+				A struct {
+					A int `json:"a"`
+				}
+				B struct {
+					B int `json:"b"`
+				}
+			}{},
+		},
+		{
+			name:     "PtrHeadIntMultiFieldsNotRoot",
+			expected: `{"A":{"a":1},"B":{"b":2}}`,
+			data: &struct {
+				A struct {
+					A int `json:"a"`
+				}
+				B struct {
+					B int `json:"b"`
+				}
+			}{A: struct {
+				A int `json:"a"`
+			}{A: 1}, B: struct {
+				B int `json:"b"`
+			}{B: 2}},
+		},
+		{
+			name:     "PtrHeadIntPtrMultiFieldsNotRoot",
+			expected: `{"A":{"a":1},"B":{"b":2}}`,
+			data: &struct {
+				A *struct {
+					A *int `json:"a"`
+				}
+				B *struct {
+					B *int `json:"b"`
+				}
+			}{A: &(struct {
+				A *int `json:"a"`
+			}{A: intptr(1)}), B: &(struct {
+				B *int `json:"b"`
+			}{B: intptr(2)})},
+		},
+		{
+			name:     "PtrHeadIntPtrNilMultiFieldsNotRoot",
+			expected: `{"A":null,"B":null}`,
+			data: &struct {
+				A *struct {
+					A *int `json:"a"`
+				}
+				B *struct {
+					B *int `json:"b"`
+				}
+			}{A: nil, B: nil},
+		},
+		{
+			name:     "PtrHeadIntNilMultiFieldsNotRoot",
+			expected: `null`,
+			data: (*struct {
+				A *struct {
+					A *int `json:"a"`
+				}
+				B *struct {
+					B *int `json:"b"`
+				}
+			})(nil),
+		},
+		{
+			name:     "PtrHeadIntDoubleMultiFieldsNotRoot",
+			expected: `{"A":{"a":1,"b":2},"B":{"a":3,"b":4}}`,
+			data: &struct {
+				A *struct {
+					A int `json:"a"`
+					B int `json:"b"`
+				}
+				B *struct {
+					A int `json:"a"`
+					B int `json:"b"`
+				}
+			}{A: &(struct {
+				A int `json:"a"`
+				B int `json:"b"`
+			}{A: 1, B: 2}), B: &(struct {
+				A int `json:"a"`
+				B int `json:"b"`
+			}{A: 3, B: 4})},
+		},
+		{
+			name:     "PtrHeadIntNilDoubleMultiFieldsNotRoot",
+			expected: `{"A":null,"B":null}`,
+			data: &struct {
+				A *struct {
+					A int `json:"a"`
+					B int `json:"b"`
+				}
+				B *struct {
+					A int `json:"a"`
+					B int `json:"b"`
+				}
+			}{A: nil, B: nil},
+		},
+		{
+			name:     "PtrHeadIntNilDoubleMultiFieldsNotRoot",
+			expected: `null`,
+			data: (*struct {
+				A *struct {
+					A int `json:"a"`
+					B int `json:"b"`
+				}
+				B *struct {
+					A int `json:"a"`
+					B int `json:"b"`
+				}
+			})(nil),
+		},
+		{
+			name:     "PtrHeadIntPtrDoubleMultiFieldsNotRoot",
+			expected: `{"A":{"a":1,"b":2},"B":{"a":3,"b":4}}`,
+			data: &struct {
+				A *struct {
+					A *int `json:"a"`
+					B *int `json:"b"`
+				}
+				B *struct {
+					A *int `json:"a"`
+					B *int `json:"b"`
+				}
+			}{A: &(struct {
+				A *int `json:"a"`
+				B *int `json:"b"`
+			}{A: intptr(1), B: intptr(2)}), B: &(struct {
+				A *int `json:"a"`
+				B *int `json:"b"`
+			}{A: intptr(3), B: intptr(4)})},
+		},
+		{
+			name:     "PtrHeadIntPtrNilDoubleMultiFieldsNotRoot",
+			expected: `{"A":null,"B":null}`,
+			data: &struct {
+				A *struct {
+					A *int `json:"a"`
+					B *int `json:"b"`
+				}
+				B *struct {
+					A *int `json:"a"`
+					B *int `json:"b"`
+				}
+			}{A: nil, B: nil},
+		},
+		{
+			name:     "PtrHeadIntPtrNilDoubleMultiFieldsNotRoot",
+			expected: `null`,
+			data: (*struct {
+				A *struct {
+					A *int `json:"a"`
+					B *int `json:"b"`
+				}
+				B *struct {
+					A *int `json:"a"`
+					B *int `json:"b"`
+				}
+			})(nil),
+		},
+
+		/*
+			{
+				name:     "Int8Head",
+				expected: `{"a":1}`,
+				data: struct {
+					A int8 `json:"a"`
+				}{A: 1},
+			},
+			{
+				name:     "Int8PtrHead",
+				expected: `{"a":1}`,
+				data: struct {
+					A *int8 `json:"a"`
+				}{A: int8ptr(1)},
+			},
+				{
+					name:     "Int8PtrNilHead",
+					expected: `{"a":null}`,
+					data: struct {
+						A *int8 `json:"a"`
+					}{A: nil},
+				},
+			{
+				name:     "PtrInt8Head",
+				expected: `{"a":1}`,
+				data: &struct {
+					A int8 `json:"a"`
+				}{A: 1},
+			},
+			{
+				name:     "PtrInt8PtrHead",
+				expected: `{"a":1}`,
+				data: &struct {
+					A *int8 `json:"a"`
+				}{A: int8ptr(1)},
+			},
+			{
+				name:     "Int8Field",
+				expected: `{"a":1,"b":2}`,
+				data: struct {
+					A int8 `json:"a"`
+					B int8 `json:"b"`
+				}{A: 1, B: 2},
+			},
+			{
+				name:     "Int8PtrField",
+				expected: `{"a":1,"b":2}`,
+				data: struct {
+					A *int8 `json:"a"`
+					B *int8 `json:"b"`
+				}{A: int8ptr(1), B: int8ptr(2)},
+			},
+		*/
+
+	}
+	for _, test := range tests {
+		for _, htmlEscape := range []bool{true, false} {
+			fmt.Println("name:", test.name)
+			var buf bytes.Buffer
+			enc := NewEncoder(&buf)
+			enc.SetEscapeHTML(htmlEscape)
+			if err := enc.Encode(test.data); err != nil {
+				t.Fatalf("%s(htmlEscape:%T): %s: %s", test.name, htmlEscape, test.expected, err)
+			}
+			if strings.TrimRight(buf.String(), "\n") != test.expected {
+				t.Fatalf("%s(htmlEscape:%T): expected %q but got %q", test.name, htmlEscape, test.expected, buf.String())
+			}
+		}
+	}
+}
diff --git a/encode_vm.go b/encode_vm.go
index 6f816b1..0b495ac 100644
--- a/encode_vm.go
+++ b/encode_vm.go
@@ -1259,12 +1259,8 @@ func (e *Encoder) run(ctx *encodeRuntimeContext, b []byte, code *opcode) ([]byte
 		case opStructFieldHeadInt:
 			ptr := load(ctxptr, code.idx)
 			if ptr == 0 {
-				if code.op == opStructFieldPtrHeadInt {
-					b = encodeNull(b)
-					b = encodeComma(b)
-				} else {
-					b = append(b, '{', '}', ',')
-				}
+				b = encodeNull(b)
+				b = encodeComma(b)
 				code = code.end.next
 			} else {
 				b = append(b, '{')
@@ -1302,12 +1298,8 @@ func (e *Encoder) run(ctx *encodeRuntimeContext, b []byte, code *opcode) ([]byte
 		case opStructEscapedFieldHeadInt:
 			ptr := load(ctxptr, code.idx)
 			if ptr == 0 {
-				if code.op == opStructEscapedFieldPtrHeadInt {
-					b = encodeNull(b)
-					b = encodeComma(b)
-				} else {
-					b = append(b, '{', '}', ',')
-				}
+				b = encodeNull(b)
+				b = encodeComma(b)
 				code = code.end.next
 			} else {
 				b = append(b, '{')