Accept prefixed xml attributes with null value

This changes makes PrefixedAttribute work the same way as
UnprefixedAttribute with respect to null values:

<t p:a={ null: String }/> is accepted and results in <t/>

1 files changed, 9 insertions, 6 deletions

diff --git a/src/library/scala/xml/PrefixedAttribute.scala b/src/library/scala/xml/PrefixedAttribute.scala
index 436dfcda43..b80d6a1c73 100644
--- a/src/library/scala/xml/PrefixedAttribute.scala
+++ b/src/library/scala/xml/PrefixedAttribute.scala
@@ -13,22 +13,25 @@ package scala.xml
  *
  *  @param pre   ...
  *  @param key   ...
- *  @param value the attribute value, which may not be null
+ *  @param value the attribute value
  *  @param next  ...
  */
 class PrefixedAttribute(
   val pre: String,
   val key: String,
   val value: Seq[Node],
-  val next: MetaData)
+  val next1: MetaData)
 extends Attribute
 {
-  if (value eq null)
-    throw new UnsupportedOperationException("value is null")
+  val next = if (value ne null) next1 else next1.remove(key)
 
-  /** same as this(key, Utility.parseAttributeValue(value), next) */
+  /** same as this(pre, key, Text(value), next), or no attribute if value is null */
   def this(pre: String, key: String, value: String, next: MetaData) =
-    this(pre, key, Text(value), next)
+    this(pre, key, if (value ne null) Text(value) else null: NodeSeq, next)
+
+  /** same as this(pre, key, value.get, next), or no attribute if value is None */
+  def this(pre: String, key: String, value: Option[Seq[Node]], next: MetaData) =
+    this(pre, key, value.orNull, next)
 
   /** Returns a copy of this unprefixed attribute with the given
    *  next field.