public MultiPartSpecBuilder charset(Charset charset) {
        Validate.notNull(charset, "Charset cannot be null");
        this.charset = charset.toString();
        return this;
    }
public MultiPartSpecBuilder charset(Charset charset) {
        Validate.notNull(charset, "Charset cannot be null");
        this.charset = charset.toString();
        return this;
    }
public MultiPartSpecBuilder charset ( Charset charset ) { Validate . notNull ( charset , "Charset cannot be null" ) ; this . charset = charset . toString ( ) ; return this ; }
Specify the charset for this charset.

@param charset The charset to use
@return An instance of MultiPartSpecBuilder
Specify the charset for this charset .