code: private MethodHandle nullChecker(Class<?> javaType)
      {
          if (javaType == Long.class) {
              return CHECK_LONG_IS_NOT_NULL;
          }
          else if (javaType == Double.class) {
              return CHECK_DOUBLE_IS_NOT_NULL;
          }
          else if (javaType == Boolean.class) {
              return CHECK_BOOLEAN_IS_NOT_NULL;
          }
          else if (javaType == Slice.class) {
              return CHECK_SLICE_IS_NOT_NULL;
          }
          else if (javaType == Block.class) {
              return CHECK_BLOCK_IS_NOT_NULL;
          }
          else {
              throw new IllegalArgumentException("Unknown java type " + javaType);
          }
      }
docs: Returns a null checker MethodHandle that only returns the value when it is not null.
  <p>
  The signature of the returned MethodHandle could be one of the following depending on javaType:
  <ul>
  <li>(Long value)long
  <li>(Double value)double
  <li>(Boolean value)boolean
  <li>(Slice value)Slice
  <li>(Block value)Block
  </ul>