rest-assured/src/main/java/io/restassured/config/MultiPartConfig.java
public MultiPartConfig defaultSubtype(String defaultSubtype) {
        return new MultiPartConfig(defaultControlName, defaultFileName, defaultSubtype, defaultBoundary, defaultCharset, true);
    }
public MultiPartConfig defaultSubtype(String defaultSubtype) {
        return new MultiPartConfig(defaultControlName, defaultFileName, defaultSubtype, defaultBoundary, defaultCharset, true);
    }
Specify the default subtype to use if not defined explicitly in when making the multi-part request.
This will control how the Content-Type will be constructed for multipart requests when using REST Assured
when no Content-Type header has been explicitly defined. For example if subtype is set to "mixed" then the
Content-Type header will be "multipart/mixed" if not specified explicitly.
<p>
Default is {@value #DEFAULT_SUBTYPE}
</p>

@param defaultSubtype The default subtype to use in multipart requests. Default is {@value #DEFAULT_SUBTYPE}.
@return A new instance of {@link MultiPartConfig}