Added correct parse of IS [NOT] NULL

fixed crash of parsing following code (from unittest):
IF V_BUF IS NULL THEN
null;
end if;

pmd-plsql/etc/grammar/PldocAST.jjt

@@ -38,6 +38,12 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  * Andreas Dangel 11/2016
  */
 
+ /**
+ * Added ASTIsNullCondition node
+ *
+ * Sergey Yanzin 11/2016
+ */
+
 //
 options {
 	DEBUG_PARSER = false ;
@@ -1972,12 +1978,33 @@ ASTUnaryExpressionNotPlusMinus UnaryExpressionNotPlusMinus() :
   (<NOT>) {sb.append(" NOT "); } 
   (simpleNode = UnaryExpression(false) ) { sb.append(simpleNode.getImage()); }
   |
-   (simpleNode = IsOfTypeCondition() ) {sb.append(simpleNode.getImage()); }
+   (simpleNode = IsNullCondition() ) {sb.append(simpleNode.getImage()); } 
   )
  { 
  jjtThis.setImage(sb.toString()); return jjtThis; 
  }
 }
+ASTIsNullCondition IsNullCondition() :  //yanzin
+{ PLSQLNode simpleNode = null; PLSQLNode name = null; StringBuilder sb = new StringBuilder(); }
+{
+  (
+    LOOKAHEAD(<IDENTIFIER> <IS> (<NOT> <NULL>|<NULL>))
+    (
+		(name = Name()) {sb.append(name.getImage());} <IS> {sb.append(" IS");} [<NOT> {sb.append(" NOT");}] <NULL> {sb.append(" NULL");} 
+	)
+	|
+	(
+		simpleNode = IsOfTypeCondition() 
+	) 
+	{ 
+		sb.append(simpleNode.getImage()); 
+	}
+  )
+  {
+    jjtThis.setImage(sb.toString());
+	return jjtThis;
+ }
+}
 
 ASTIsOfTypeCondition IsOfTypeCondition() :
 { PLSQLNode simpleNode = null; PLSQLNode name = null; StringBuilder sb = new StringBuilder(); }

pmd-plsql/src/main/java/net/sourceforge/pmd/lang/plsql/rule/AbstractPLSQLRule.java

@@ -789,6 +789,11 @@ public abstract class AbstractPLSQLRule extends AbstractRule implements PLSQLPar
         return visit((PLSQLNode) node, data);
 	}
 
+	@Override
+	public Object visit(ASTIsNullCondition node, Object data) {
+        return visit((PLSQLNode) node, data);
+	}
+
   /*
    * Treat all Executable Code 
    */

pmd-plsql/src/test/java/net/sourceforge/pmd/lang/plsql/PLSQLParserTest.java

@@ -60,4 +60,9 @@ public class PLSQLParserTest extends AbstractPLSQLParserTst {
     public void testBug1520Using() throws Exception {
         parsePLSQL(IOUtils.toString(PLSQLParserTest.class.getResourceAsStream("ast/Using.pls")));
     }
+
+    @Test
+    public void testIsNull() throws Exception {
+        parsePLSQL(IOUtils.toString(PLSQLParserTest.class.getResourceAsStream("ast/IsNull.pls")));
+    }
 }

pmd-plsql/src/test/resources/net/sourceforge/pmd/lang/plsql/ast/IsNull.pls

@@ -0,0 +1,16 @@
+PROCEDURE IsNull (
+  dummy IN number
+)
+is
+  V_BUF varchar(1);
+BEGIN
+
+IF V_BUF IS NULL THEN
+  null;
+end if;
+
+IF V_BUF IS NOT NULL THEN
+  null;
+end if;
+
+end;