rest-assured/src/main/java/io/restassured/builder/MultiPartSpecBuilder.java
public MultiPartSpecBuilder charset(String charset) {
        Validate.notEmpty(charset, "Charset cannot be empty");
        if (content instanceof byte[] || content instanceof InputStream) {
            throw new IllegalArgumentException("Cannot specify charset input streams or byte arrays.");
        }
        this.charset = charset;
        return this;
    }
public MultiPartSpecBuilder charset(String charset) {
        Validate.notEmpty(charset, "Charset cannot be empty");
        if (content instanceof byte[] || content instanceof InputStream) {
            throw new IllegalArgumentException("Cannot specify charset input streams or byte arrays.");
        }
        this.charset = charset;
        return this;
    }
Specify the charset for this charset.

@param charset The charset to use
@return An instance of MultiPartSpecBuilder