Use explicit null to clear issue types

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: ea8faa5c-7f26-4e2d-bf9c-6f0b5f173e8c

Author: zwick

README.md

@@ -941,7 +941,7 @@ The following sets of tools are available:
   - `state`: New state (string, optional)
   - `state_reason`: Reason for the state change. Ignored unless state is changed. (string, optional)
   - `title`: Issue title (string, optional)
-  - `type`: Type of this issue. For updates, use an empty string to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string, optional)
+  - `type`: Type of this issue. For updates, pass null to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string | null, optional)
 
 - **list_issue_fields** - List issue fields
   - **Required OAuth Scopes (any of)**: `repo`, `read:org`

cmd/github-mcp-server/generate_docs.go

@@ -273,19 +273,7 @@ func writeToolDoc(buf *strings.Builder, tool inventory.ServerTool) {
 				requiredStr = "required"
 			}
 
-			var typeStr string
-
-			// Get the type and description
-			switch prop.Type {
-			case "array":
-				if prop.Items != nil {
-					typeStr = prop.Items.Type + "[]"
-				} else {
-					typeStr = "array"
-				}
-			default:
-				typeStr = prop.Type
-			}
+			typeStr := schemaTypeString(prop)
 
 			// Indent any continuation lines in the description to maintain markdown formatting
 			description := indentMultilineDescription(prop.Description, "    ")
@@ -300,6 +288,37 @@ func writeToolDoc(buf *strings.Builder, tool inventory.ServerTool) {
 	}
 }
 
+func schemaTypeString(schema *jsonschema.Schema) string {
+	if schema == nil {
+		return ""
+	}
+	if schema.Type == "array" {
+		if schema.Items != nil {
+			return schema.Items.Type + "[]"
+		}
+		return "array"
+	}
+	if schema.Type != "" {
+		return schema.Type
+	}
+	if len(schema.Types) > 0 {
+		return strings.Join(schema.Types, " | ")
+	}
+
+	union := schema.AnyOf
+	if len(union) == 0 {
+		union = schema.OneOf
+	}
+	types := make([]string, 0, len(union))
+	for _, member := range union {
+		memberType := schemaTypeString(member)
+		if memberType != "" && !slices.Contains(types, memberType) {
+			types = append(types, memberType)
+		}
+	}
+	return strings.Join(types, " | ")
+}
+
 // scopesEqual checks if two scope slices contain the same elements (order-independent)
 func scopesEqual(a, b []string) bool {
 	if len(a) != len(b) {

cmd/github-mcp-server/main_test.go

@@ -5,6 +5,7 @@ import (
 	"path/filepath"
 	"testing"
 
+	"github.com/google/jsonschema-go/jsonschema"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -36,3 +37,53 @@ func TestGitHubAppFlagsAreStdioOnly(t *testing.T) {
 	assert.NotNil(t, stdioCmd.Flags().Lookup("app-id"))
 	assert.Nil(t, httpCmd.Flags().Lookup("app-id"))
 }
+
+func TestSchemaTypeString(t *testing.T) {
+	tests := []struct {
+		name   string
+		schema *jsonschema.Schema
+		want   string
+	}{
+		{name: "type", schema: &jsonschema.Schema{Type: "string"}, want: "string"},
+		{name: "types", schema: &jsonschema.Schema{Types: []string{"string", "number"}}, want: "string | number"},
+		{
+			name: "anyOf",
+			schema: &jsonschema.Schema{AnyOf: []*jsonschema.Schema{
+				{Type: "string"},
+				{Type: "null"},
+			}},
+			want: "string | null",
+		},
+		{
+			name: "oneOf",
+			schema: &jsonschema.Schema{OneOf: []*jsonschema.Schema{
+				{Type: "number"},
+				{Type: "string"},
+			}},
+			want: "number | string",
+		},
+		{
+			name:   "array",
+			schema: &jsonschema.Schema{Type: "array", Items: &jsonschema.Schema{Type: "string"}},
+			want:   "string[]",
+		},
+		{
+			name: "union array preserves existing rendering",
+			schema: &jsonschema.Schema{
+				Type: "array",
+				Items: &jsonschema.Schema{AnyOf: []*jsonschema.Schema{
+					{Type: "string"},
+					{Type: "object"},
+				}},
+			},
+			want: "[]",
+		},
+		{name: "untyped array", schema: &jsonschema.Schema{Type: "array"}, want: "array"},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			assert.Equal(t, tc.want, schemaTypeString(tc.schema))
+		})
+	}
+}

docs/feature-flags.md

@@ -71,7 +71,7 @@ runtime behavior (such as output formatting) won't appear here.
   - `state`: New state (string, optional)
   - `state_reason`: Reason for the state change. Ignored unless state is changed. (string, optional)
   - `title`: Issue title (string, optional)
-  - `type`: Type of this issue. For updates, use an empty string to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string, optional)
+  - `type`: Type of this issue. For updates, pass null to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string | null, optional)
 
 - **ui_get** - Get UI data
   - **Required OAuth Scopes (any of)**: `repo`, `read:org`
@@ -200,7 +200,7 @@ runtime behavior (such as output formatting) won't appear here.
   - `confidence`: How confident you are in this choice. Use 'HIGH' for clear signal or explicit user request, 'MEDIUM' for reasonable inference with some ambiguity, 'LOW' for best guess with limited signal. (string, optional)
   - `is_suggestion`: If true, this issue type change is sent to the API as a suggestion (suggest:true) rather than an applied value. Whether the type is applied or recorded as a proposal is determined by the API. (boolean, optional)
   - `issue_number`: The issue number to update (number, required)
-  - `issue_type`: The issue type to set, or an empty string to remove the current type (string, required)
+  - `issue_type`: The issue type to set, or null to remove the current type (string | null, required)
   - `owner`: Repository owner (username or organization) (string, required)
   - `rationale`: One concise sentence explaining what specifically about the issue led you to choose this type. State the concrete signal (e.g. 'Reports a crash when saving' → bug, 'Asks for dark mode support' → feature). (string, optional)
   - `repo`: Repository name (string, required)

docs/insiders-features.md

@@ -65,7 +65,7 @@ The list below is generated from the Go source. It covers tool **inventory and s
   - `state`: New state (string, optional)
   - `state_reason`: Reason for the state change. Ignored unless state is changed. (string, optional)
   - `title`: Issue title (string, optional)
-  - `type`: Type of this issue. For updates, use an empty string to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string, optional)
+  - `type`: Type of this issue. For updates, pass null to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string | null, optional)
 
 - **ui_get** - Get UI data
   - **Required OAuth Scopes (any of)**: `repo`, `read:org`

pkg/github/__toolsnaps__/issue_write.snap

@@ -120,8 +120,16 @@
         "type": "string"
       },
       "type": {
-        "description": "Type of this issue. For updates, use an empty string to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter.",
-        "type": "string"
+        "anyOf": [
+          {
+            "minLength": 1,
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "description": "Type of this issue. For updates, pass null to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter."
       }
     },
     "required": [

pkg/github/__toolsnaps__/update_issue_type.snap

@@ -6,7 +6,7 @@
     "readOnlyHint": false,
     "title": "Update Issue Type"
   },
-  "description": "Set or remove the type of an existing issue. Use an empty issue_type to remove the current type. When setting a value, include a confidence level (LOW, MEDIUM, or HIGH) reflecting how certain you are about the choice.",
+  "description": "Set or remove the type of an existing issue. Pass null to remove the current type. When setting a value, include a confidence level (LOW, MEDIUM, or HIGH) reflecting how certain you are about the choice.",
   "inputSchema": {
     "properties": {
       "confidence": {
@@ -28,8 +28,16 @@
         "type": "number"
       },
       "issue_type": {
-        "description": "The issue type to set, or an empty string to remove the current type",
-        "type": "string"
+        "anyOf": [
+          {
+            "minLength": 1,
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "description": "The issue type to set, or null to remove the current type"
       },
       "owner": {
         "description": "Repository owner (username or organization)",

pkg/github/granular_tools_test.go

@@ -3,6 +3,7 @@ package github
 import (
 	"context"
 	"encoding/json"
+	"maps"
 	"net/http"
 	"strings"
 	"testing"
@@ -756,7 +757,11 @@ func TestGranularUpdateIssueMilestone(t *testing.T) {
 
 func TestGranularUpdateIssueType(t *testing.T) {
 	toolSchema := GranularUpdateIssueType(translations.NullTranslationHelper).Tool.InputSchema.(*jsonschema.Schema)
-	assert.Equal(t, "string", toolSchema.Properties["issue_type"].Type)
+	issueTypeSchema := toolSchema.Properties["issue_type"]
+	require.Len(t, issueTypeSchema.AnyOf, 2)
+	assert.Equal(t, "string", issueTypeSchema.AnyOf[0].Type)
+	assert.Equal(t, 1, *issueTypeSchema.AnyOf[0].MinLength)
+	assert.Equal(t, "null", issueTypeSchema.AnyOf[1].Type)
 
 	tests := []struct {
 		name        string
@@ -792,12 +797,12 @@ func TestGranularUpdateIssueType(t *testing.T) {
 			},
 		},
 		{
-			name: "remove type with empty string",
+			name: "remove type with null",
 			requestArgs: map[string]any{
 				"owner":        "owner",
 				"repo":         "repo",
 				"issue_number": float64(1),
-				"issue_type":   "",
+				"issue_type":   nil,
 			},
 			expectedReq: map[string]any{
 				"type": nil,
@@ -823,6 +828,23 @@ func TestGranularUpdateIssueType(t *testing.T) {
 	}
 }
 
+func TestGranularUpdateIssueTypeRejectsEmptyIssueType(t *testing.T) {
+	deps := BaseDeps{Client: mustNewGHClient(t, MockHTTPClientWithHandlers(nil))}
+	serverTool := GranularUpdateIssueType(translations.NullTranslationHelper)
+	handler := serverTool.Handler(deps)
+	request := createMCPRequest(map[string]any{
+		"owner":        "owner",
+		"repo":         "repo",
+		"issue_number": float64(1),
+		"issue_type":   "",
+	})
+
+	result, err := handler(ContextWithDeps(context.Background(), deps), &request)
+	require.NoError(t, err)
+	errorContent := getErrorResult(t, result)
+	assert.Contains(t, errorContent.Text, "parameter issue_type must not be empty")
+}
+
 func TestGranularUpdateIssueTypeRejectsMissingIssueType(t *testing.T) {
 	deps := BaseDeps{Client: mustNewGHClient(t, MockHTTPClientWithHandlers(nil))}
 	serverTool := GranularUpdateIssueType(translations.NullTranslationHelper)
@@ -840,6 +862,38 @@ func TestGranularUpdateIssueTypeRejectsMissingIssueType(t *testing.T) {
 	assert.Contains(t, errorContent.Text, "missing required parameter: issue_type")
 }
 
+func TestGranularUpdateIssueTypeRejectsMetadataWhenRemovingType(t *testing.T) {
+	tests := []struct {
+		name string
+		args map[string]any
+	}{
+		{name: "rationale", args: map[string]any{"rationale": "live validation"}},
+		{name: "confidence", args: map[string]any{"confidence": "HIGH"}},
+		{name: "suggestion", args: map[string]any{"is_suggestion": true}},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			deps := BaseDeps{}
+			serverTool := GranularUpdateIssueType(translations.NullTranslationHelper)
+			handler := serverTool.Handler(deps)
+			args := map[string]any{
+				"owner":        "owner",
+				"repo":         "repo",
+				"issue_number": float64(1),
+				"issue_type":   nil,
+			}
+			maps.Copy(args, tc.args)
+			request := createMCPRequest(args)
+
+			result, err := handler(ContextWithDeps(context.Background(), deps), &request)
+			require.NoError(t, err)
+			errorContent := getErrorResult(t, result)
+			assert.Contains(t, errorContent.Text, "suggestion metadata is not supported when removing an issue type; omit rationale, confidence, and is_suggestion")
+		})
+	}
+}
+
 func TestGranularUpdateIssueTypeSuggest(t *testing.T) {
 	tests := []struct {
 		name        string

pkg/github/issues.go

@@ -2150,8 +2150,11 @@ Options are:
 						Description: "Milestone number",
 					},
 					"type": {
-						Type:        "string",
-						Description: "Type of this issue. For updates, use an empty string to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter.",
+						AnyOf: []*jsonschema.Schema{
+							{Type: "string", MinLength: jsonschema.Ptr(1)},
+							{Type: "null"},
+						},
+						Description: "Type of this issue. For updates, pass null to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter.",
 					},
 					"state": {
 						Type:        "string",
@@ -2226,8 +2229,8 @@ Options are:
 			// execute now (see shouldDeferToForm).
 			deferToForm := shouldDeferToForm(ctx, deps, req, args, issueWriteFormParams)
 			if method == "update" {
-				if issueType, ok := args["type"].(string); ok && issueType == "" {
-					// The form replaces an empty type with the current type, so execute
+				if issueType, ok := args["type"]; ok && issueType == nil {
+					// The form replaces a null type with the current type, so execute
 					// directly to preserve the clear and any co-submitted values.
 					deferToForm = false
 				}
@@ -2283,10 +2286,14 @@ Options are:
 			}
 
 			// Get optional type
-			issueType, issueTypeProvided, err := OptionalParamOK[string](args, "type")
+			issueTypeParam, issueTypeProvided, err := OptionalNullableStringParam(args, "type")
 			if err != nil {
 				return utils.NewToolResultError(err.Error()), nil, nil
 			}
+			issueType := ""
+			if issueTypeParam != nil {
+				issueType = *issueTypeParam
+			}
 
 			// Handle state, state_reason and duplicateOf parameters
 			state, err := OptionalParam[string](args, "state")
@@ -2415,7 +2422,7 @@ type UpdateIssueOptions struct {
 	AssigneesProvided bool
 	// LabelsProvided sends the labels field even when the slice is empty.
 	LabelsProvided bool
-	// IssueTypeProvided sends the type field, including an explicit clear for an empty value.
+	// IssueTypeProvided sends the type field, including an explicit clear.
 	IssueTypeProvided bool
 }