guava/src/com/google/common/net/MediaType.java
public MediaType withParameter(String attribute, String value) {
    return withParameters(attribute, ImmutableSet.of(value));
  }
public MediaType withParameter(String attribute, String value) {
    return withParameters(attribute, ImmutableSet.of(value));
  }
<em>Replaces</em> all parameters with the given attribute with a single parameter with the
given value. If multiple parameters with the same attributes are necessary use {@link
#withParameters(String, Iterable)}. Prefer {@link #withCharset} for setting the {@code charset}
parameter when using a {@link Charset} object.

@throws IllegalArgumentException if either {@code attribute} or {@code value} is invalid