code: public void removeProp(String key) {
      this.specProperties.remove(key);
      if (this.commonProperties.containsKey(key)) {
        // This case should not happen.
        Properties commonPropsCopy = new Properties();
        commonPropsCopy.putAll(this.commonProperties);
        commonPropsCopy.remove(key);
        this.commonProperties = commonPropsCopy;
      }
    }
docs: Remove a property if it exists.
  
  @param key property key