logback-android/src/main/java/ch/qos/logback/core/joran/spi/InterpretationContext.java
public String getProperty(String key) {
    String v = propertiesMap.get(key);
    if (v != null) {
      return v;
    } else {
      return context.getProperty(key);
    }
  }
public String getProperty(String key) {
    String v = propertiesMap.get(key);
    if (v != null) {
      return v;
    } else {
      return context.getProperty(key);
    }
  }
If a key is found in propertiesMap then return it. Otherwise, delegate to
the context.