Add uc4-beam-flink

Also excption Exception in thread main java.lang.IllegalArgumentException:
 Cannot union streams of different types:
  CoderTypeInformation{coder=WindowedValue$
  FullWindowedValueCoder(KvCoder(NullableCoder(StringUtf8Coder)
  ,org.apache.beam.sdk.coders.AvroCoder@b03f3cea),IntervalWindow)}
  and
  CoderTypeInformation{coder=WindowedValue$
  FullWindowedValueCoder(KvCoder(NullableCoder(StringUtf8Coder)
  ,NullableCoder(org.apache.beam.sdk.coders.AvroCoder@b03f3cea)),IntervalWindow)}
 by just using the raw not NullableCoder