protected void setFieldSeparator(String fieldSeparator) {
        if (fieldSeparator == null) {
            fieldSeparator = "";
        }
        this.fieldSeparator = fieldSeparator;
    }
<p>Sets the field separator text.</p>

<p><code>null</code> is accepted, but will be converted to
an empty String.</p>

@param fieldSeparator  the new field separator text
android/android_framework/base/src/main/java/lang3/builder/ToStringStyle.java