static Boolean opAnd(Boolean... ops) {
    // When people forget to quote a string, op1/op2 is null.
    // For example, select * from some_table where ds > 2012-12-1 and ds < 2012-12-2 .
    boolean anyNull = false;
    for (Boolean op : ops) {
      if (op == null) {
        anyNull = true;
        continue;
      }
      if (op.equals(Boolean.FALSE)) {
        return Boolean.FALSE;
      }
    }
    if (anyNull) {
      return null;
    }
    return Boolean.TRUE;
  }
Expression processor factory for partition condition removing. Each processor tries to
calculate a result vector from its children's result vectors.
Each element is the result for one of the pruned partitions.
It also generates node by Modifying expr trees with partition conditions removed
ql/src/java/org/apache/hadoop/hive/ql/optimizer/pcr/PcrExprProcFactory.java