code: def _unify_type(self, t):
      if self._ret_type is None:
          self._ret_type = t
      else:
          r = unify_types_limited(self._ret_type, t)
          if not r:
              raise TypeError(
                  "'then' expressions must have same type, found '{}' and '{}'".format(
                      self._ret_type, t
                  )
              )
  
imports: import hail
  from hail.typecheck import typecheck_method
  from hail.expr.expressions import unify_types, unify_types_limited, expr_any, expr_bool, ExpressionException, construct_expr, expr_str
  from hail import ir
label_desc: Use image node_id 2 for calling the ConditionalBuilder obj's underlying member method code with example usage: obj._unify_type(t) without return types