code: boolean isNestedProperty(String propertyName) {
      Preconditions.checkNotNull(propertyName);
      return propertyName.contains(SEPARATOR) && !propertyName.startsWith(SEPARATOR) && !propertyName.endsWith(SEPARATOR);
    }
docs: Returns {@code true} if property is nested, {@code false} otherwise.
  <p/>
  Examples:
  <pre>
  isNestedProperty(&quot;address.street&quot;); // true
  isNestedProperty(&quot;address.street.name&quot;); // true
  isNestedProperty(&quot;person&quot;); // false
  isNestedProperty(&quot;.name&quot;); // false
  isNestedProperty(&quot;person.&quot;); // false
  isNestedProperty(&quot;person.name.&quot;); // false
  isNestedProperty(&quot;.person.name&quot;); // false
  isNestedProperty(&quot;.&quot;); // false
  isNestedProperty(&quot;&quot;); // false
  </pre>
  
  @param propertyName the given property name.
  @return {@code true} if property is nested, {@code false} otherwise.
  @throws NullPointerException if given property name is {@code null}.