fix def of EMPTY->INVALID

runtime/Java/src/org/antlr/v4/runtime/ParserRuleContext.java

@@ -294,7 +294,7 @@ public class ParserRuleContext<Symbol extends Token> extends RuleContext {
 
 	@Override
 	public Interval getSourceInterval() {
-		if ( start==null || stop==null ) return Interval.EMPTY;
+		if ( start==null || stop==null ) return Interval.INVALID;
 		return Interval.of(start.getTokenIndex(), stop.getTokenIndex());
 	}
 
@@ -305,7 +305,7 @@ public class ParserRuleContext<Symbol extends Token> extends RuleContext {
 	 */
 	public String getText(TokenStream tokens) {
 		Interval range = getSourceInterval();
-		return range==Interval.EMPTY ? null : tokens.toString(range.a, range.b);
+		return range==Interval.INVALID ? null : tokens.toString(range.a, range.b);
 	}
 
 	public Symbol getStart() { return start; }

runtime/Java/src/org/antlr/v4/runtime/RuleContext.java

@@ -212,7 +212,7 @@ public class RuleContext implements ParseTree.RuleNode {
 
 	@Override
 	public Interval getSourceInterval() {
-		return Interval.EMPTY;
+		return Interval.INVALID;
 	}
 
 	@Override

runtime/Java/src/org/antlr/v4/runtime/misc/Interval.java

@@ -33,7 +33,6 @@ public class Interval {
 	public static final int INTERVAL_POOL_MAX_VALUE = 1000;
 
 	public static final Interval INVALID = new Interval(-1,-2);
-	public static final Interval EMPTY = new Interval(0,-1); // len 0
 
 	static Interval[] cache = new Interval[INTERVAL_POOL_MAX_VALUE+1];
 

runtime/Java/src/org/antlr/v4/runtime/tree/SyntaxTree.java

@@ -41,7 +41,7 @@ public interface SyntaxTree extends Tree {
 	 *  node is a leaf, then the interval represents a single token.
 	 *
 	 *  If source interval is unknown, this does not return null.
-	 *  It returns an interval of length 0: Interval.EMPTY.
+	 *  It returns Interval.INVALID.
 	 */
 	Interval getSourceInterval();
 }