Humanizr/Humanizer · error · InvalidOperationException

Expected JSON object.

Error message

Expected JSON object.

What it means

CreateTargetTypedConstructorExpression (GenerationHelpers.cs:403-408) emits a target-typed 'new(...)' constructor call from a JSON object's properties. It throws when the supplied element is not a JSON Object (e.g. an array or scalar), because constructor arguments are read from object properties.

Source

Thrown at src/Humanizer.SourceGenerators/Common/GenerationHelpers.cs:407

                builder.Append(", ");
            }

            builder.Append("[TimeUnit.");
            builder.Append(ToEnumMemberName(entry.Name));
            builder.Append("] = GrammaticalGender.");
            builder.Append(ToEnumMemberName(entry.Value.GetString()!));
            first = false;
        }

        builder.Append(" }.ToFrozenDictionary()");
        return builder.ToString();
    }

    static string CreateTargetTypedConstructorExpression(JsonElement element, params JsonConstructorValueEmitter[] emitters)
    {
        if (element.ValueKind != JsonValueKind.Object)
        {
            throw new InvalidOperationException("Expected JSON object.");
        }

        var builder = new StringBuilder("new(");
        AppendConstructorValues(builder, element, emitters);
        builder.Append(')');
        return builder.ToString();
    }

    static string CreateTypedConstructorArrayExpression(string elementTypeName, JsonElement arrayElement, params JsonConstructorValueEmitter[] emitters)
    {
        if (arrayElement.ValueKind != JsonValueKind.Array)
        {
            throw new InvalidOperationException("Expected JSON array.");
        }

        var builder = new StringBuilder("new ");
        builder.Append(elementTypeName);
        builder.Append("[] { ");

View on GitHub (pinned to ffc2b77c0f)

Solutions

1. Ensure the element at the contract's sourcePath is a JSON object.
2. Correct the contract member kind (e.g. use the array constructor emitter) if the data is genuinely a list.
3. Fix the sourcePath to reference the single object node.

Example fix

// before - array where object expected
[ { "base": 10 } ]
// after - object
{ "base": 10 }

// Target-typed constructor input must be a JSON object (C#)
if (element.ValueKind != JsonValueKind.Object)
    throw new InvalidOperationException("Expected JSON object for constructor expression");

static bool IsJsonObject(JsonElement el) => el.ValueKind == JsonValueKind.Object;

When it happens

Trigger: A contract member that should be a single object is given a JSON array or scalar at its sourcePath.

Common situations: A contract sourcePath points at a list where a single record is expected; data reshaped so a record became an array; wrong member kind declared in the contract.

Related errors

• Property '{propertyName}' must be an integer.
• Indexed string arrays require string values. Property '{prop
• Missing required property '{sourcePath}'.
• Missing required property '{propertyName}'.
• Expected JSON array.

AI-assisted analysis of Humanizr/Humanizer@ffc2b77c0f (2026-08-13). Data as JSON: /api/errors/0fce7dcc0ca7e252. Report an issue: GitHub.