[FLINK-8278] [docs] Fix Scala examples of metrics docs (var initialization).

docs/dev/stream/state/state.md

@@ -397,7 +397,7 @@ class BufferingSink(threshold: Int = 0)
     with CheckpointedRestoring[List[(String, Int)]] {
 
   @transient
-  private var checkpointedState: ListState[(String, Int)] = null
+  private var checkpointedState: ListState[(String, Int)] = _
 
   private val bufferedElements = ListBuffer[(String, Int)]()
 

docs/monitoring/metrics.md

@@ -69,7 +69,7 @@ public class MyMapper extends RichMapFunction<String, String> {
 {% highlight scala %}
 
 class MyMapper extends RichMapFunction[String,String] {
-  @transient private var counter: Counter
+  @transient private var counter: Counter = _
 
   override def open(parameters: Configuration): Unit = {
     counter = getRuntimeContext()
@@ -119,7 +119,7 @@ public class MyMapper extends RichMapFunction<String, String> {
 {% highlight scala %}
 
 class MyMapper extends RichMapFunction[String,String] {
-  @transient private var counter: Counter
+  @transient private var counter: Counter = _
 
   override def open(parameters: Configuration): Unit = {
     counter = getRuntimeContext()
@@ -229,7 +229,7 @@ public class MyMapper extends RichMapFunction<Long, Long> {
 {% highlight scala %}
 
 class MyMapper extends RichMapFunction[Long,Long] {
-  @transient private var histogram: Histogram
+  @transient private var histogram: Histogram = _
 
   override def open(parameters: Configuration): Unit = {
     histogram = getRuntimeContext()
@@ -289,7 +289,7 @@ public class MyMapper extends RichMapFunction<Long, Long> {
 {% highlight scala %}
 
 class MyMapper extends RichMapFunction[Long, Long] {
-  @transient private var histogram: Histogram
+  @transient private var histogram: Histogram = _
 
   override def open(config: Configuration): Unit = {
     com.codahale.metrics.Histogram dropwizardHistogram =
@@ -342,7 +342,7 @@ public class MyMapper extends RichMapFunction<Long, Long> {
 {% highlight scala %}
 
 class MyMapper extends RichMapFunction[Long,Long] {
-  @transient private var meter: Meter
+  @transient private var meter: Meter = _
 
   override def open(config: Configuration): Unit = {
     meter = getRuntimeContext()
@@ -401,7 +401,7 @@ public class MyMapper extends RichMapFunction<Long, Long> {
 {% highlight scala %}
 
 class MyMapper extends RichMapFunction[Long,Long] {
-  @transient private var meter: Meter
+  @transient private var meter: Meter = _
 
   override def open(config: Configuration): Unit = {
     com.codahale.metrics.Meter dropwizardMeter = new com.codahale.metrics.Meter()