@Nullable
    public ThriftFunction function(String method) {
        return functions.get(method);
    }
Returns the {@link ThriftFunction} that provides the metadata of the specified Thrift function.

@return the {@link ThriftFunction}, or {@code null} if there's no such function.
thrift/thrift0.13/src/main/java/com/linecorp/armeria/internal/common/thrift/ThriftServiceMetadata.java