flink-instrumentation/workspace/flink-1.4.1-instrumented/flink-1.4.1/flink-core/src/main/java/org/apache/flink/util/StringUtils.java
/**
	 * If both string arguments are non-null, this method concatenates them with ' and '.
	 * If only one of the arguments is non-null, this method returns the non-null argument.
	 * If both arguments are null, this method returns null.
	 * 
	 * @param s1 The first string argument
	 * @param s2 The second string argument
	 * 
	 * @return The concatenated string, or non-null argument, or null 
	 */
If both string arguments are non-null, this method concatenates them with ' and '.
If only one of the arguments is non-null, this method returns the non-null argument.
If both arguments are null, this method returns null.

@param s1 The first string argument
@param s2 The second string argument

@return The concatenated string, or non-null argument, or null
If both string arguments are non - null this method concatenates them with ' and ' . If only one of the arguments is non - null this method returns the non - null argument . If both arguments are null this method returns null . @param s1 The first string argument @param s2 The second string argument @return The concatenated string or non - null argument or null
@Nullable
	public static String concatenateWithAnd(@Nullable String s1, @Nullable String s2) {
		if (s1 != null) {
			return s2 == null ? s1 : s1 + " and " + s2;
		}
		else {
			return s2 != null ? s2 : null;
		}
	}
@ Nullable public static String concatenateWithAnd ( @ Nullable String s1 , @ Nullable String s2 ) { if ( s1 != null ) { return s2 == null ? s1 : s1 + " and " + s2 ; } else { return s2 != null ? s2 : null ; } }
If both string arguments are non-null, this method concatenates them with ' and '.
If both string arguments are non - null this method concatenates them with ' and ' .