class DefaultModelProblem implements ModelProblem {

    private final String source;

    private final int lineNumber;

    private final int columnNumber;

    private final String modelId;

    private final String message;

    private final Exception exception;

    private final Severity severity;

    private final Version version;

    /**
     * Creates a new problem with the specified message and exception.
     *
     * @param message The message describing the problem, may be {@code null}.
     * @param severity The severity level of the problem, may be {@code null} to default to
     *            {@link Severity#ERROR}.
     * @param source The source of the problem, may be {@code null}.
     * @param lineNumber The one-based index of the line containing the error or {@code -1} if unknown.
     * @param columnNumber The one-based index of the column containing the error or {@code -1} if unknown.
     * @param exception The exception that caused this problem, may be {@code null}.
     */
    // mkleint: does this need to be public?
    public DefaultModelProblem(
            String message,
            Severity severity,
            Version version,
            Model source,
            int lineNumber,
            int columnNumber,
            Exception exception) {
        this(
                message,
                severity,
                version,
                ModelProblemUtils.toPath(source),
                lineNumber,
                columnNumber,
                ModelProblemUtils.toId(source),
                exception);
    }

    /**
     * Creates a new problem with the specified message and exception.
     *
     * @param message The message describing the problem, may be {@code null}.
     * @param severity The severity level of the problem, may be {@code null} to default to
     *            {@link Severity#ERROR}.
     * @param version The version since the problem is relevant
     * @param source A hint about the source of the problem like a file path, may be {@code null}.
     * @param lineNumber The one-based index of the line containing the problem or {@code -1} if unknown.
     * @param columnNumber The one-based index of the column containing the problem or {@code -1} if unknown.
     * @param modelId The identifier of the model that exhibits the problem, may be {@code null}.
     * @param exception The exception that caused this problem, may be {@code null}.
     */
    // mkleint: does this need to be public?
    @SuppressWarnings("checkstyle:parameternumber")
    public DefaultModelProblem(
            String message,
            Severity severity,
            Version version,
            String source,
            int lineNumber,
            int columnNumber,
            String modelId,
            Exception exception) {
        this.message = message;
        this.severity = (severity != null) ? severity : Severity.ERROR;
        this.source = (source != null) ? source : "";
        this.lineNumber = lineNumber;
        this.columnNumber = columnNumber;
        this.modelId = (modelId != null) ? modelId : "";
        this.exception = exception;
        this.version = version;
    }

    @Override
    public String getSource() {
        return source;
    }

    @Override
    public int getLineNumber() {
        return lineNumber;
    }

    @Override
    public int getColumnNumber() {
        return columnNumber;
    }

    public String getModelId() {
        return modelId;
    }

    @Override
    public Exception getException() {
        return exception;
    }

    @Override
    public String getLocation() {
        return "";
    }

    @Override
    public String getMessage() {<FILL_FUNCTION_BODY>}

    @Override
    public Severity getSeverity() {
        return severity;
    }

    public Version getVersion() {
        return version;
    }

    @Override
    public String toString() {
        StringBuilder buffer = new StringBuilder(128);

        buffer.append('[').append(getSeverity()).append("] ");
        buffer.append(getMessage());
        String location = ModelProblemUtils.formatLocation(this, null);
        if (!location.isEmpty()) {
            buffer.append(" @ ");
            buffer.append(location);
        }

        return buffer.toString();
    }
}

        String msg = null;

        if (message != null && !message.isEmpty()) {
            msg = message;
        } else if (exception != null) {
            msg = exception.getMessage();
        }

        if (msg == null) {
            msg = "";
        }

        return msg;
    
<no_super_class>