Method isNull

core/src/main/java/org/apache/calcite/rex/RexUtil.java:214–223

Returns whether a node represents the NULL value or a series of nested CAST(NULL AS type) calls. For example: isNull(CAST(CAST(NULL as INTEGER) AS VARCHAR(1))) returns true.

(RexNode expr)

   * returns {@code true}.
   */
  public static boolean isNull(RexNode expr) {
    switch (expr.getKind()) {
    case LITERAL:
      return ((RexLiteral) expr).getValue2() == null;
    case CAST:
      return isNull(((RexCall) expr).operands.get(0));
    default:
      return false;
    }
  }

  /**
   * Returns whether a node represents a {@link SqlTypeName#SYMBOL} literal.