Setting the environment variable ACCUMULO_CLIENT_CONF_PATH to a directory that exists but does not contain a file named client.conf throws
org.apache.commons.configuration.ConfigurationException: Cannot load a configuration from a directory
To demo this, simply set ACCUMULO_CLIENT_CONF_PATH to /tmp, make sure client.conf doesn't exist in /tmp and try to run the accumulo shell.
The problem is ClientConfiguration.java on line 221 checks File.canRead() which is true for a Directory and a File. The solution is to make the branch check File.isFile() && File.canRead()