src/main/java/org/jfree/graphics2d/svg/StandardFontMapper.java
public void put(String family, String alternate) {
        Args.nullNotPermitted(family, "family");
        this.alternates.put(family, alternate);
    }
public void put(String family, String alternate) {
        Args.nullNotPermitted(family, "family");
        this.alternates.put(family, alternate);
    }
Adds a font family mapping (if the specified alternate is
{@code null} it has the effect of clearing any existing mapping).

@param family  the font family name ({@code null} not permitted).
@param alternate  the alternate ({@code null} permitted).