public String getHeader(String headerName) {
        return headers.get(headerName);
    }
Looks up a header by name and returns its value. Does case insensitive comparison.

@param headerName Name of header to get value for.
@return The header value of the given header. Null if header is not present.
@deprecated See {@link #getHeaderValues(String)}
aws-java-sdk-core/src/main/java/com/amazonaws/http/HttpResponse.java