@Override
    public V get(Object key) {
      if (!containsKey(key)) {
        throw new DataVariableContextException(key.toString());
      }
      return super.get(key);
    }
Returns the current JVM's Java specification version.
Examples for valid values are {@code 1.6} and {@code 1.7}.

@return the current JVM's Java specification version
spock-core/src/main/java/org/spockframework/runtime/extension/builtin/PreconditionContext.java