When I call this method "Signature.getInstance("RSASSA-PSS").getParameters()" without initializing the Signature parameters, I get the following exception,
 
Exception java.security.ProviderException: Missing required PSS parameters
       at RSAPSSSignature.engineGetParameters (RSAPSSSignature.java:608)
       at Signature$Delegate.engineGetParameters (Signature.java:1275)
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Signature#getParamters() specification says:
"The returned parameters may contain a combination of default and randomly generated parameter values used by the underlying signature implementation if this signature requires algorithm parameters but was not initialized with any."
Specification does not state any possible exceptions being thrown.
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Also, when I check with other algorithms like “RSA”, “DSA” , this issue is not there.
For e.g.
jshell> Signature.getInstance("SHA256withDSA").getParameters()
$58 ==> null

jshell> Signature.getInstance("SHA256withRSA").getParameters()
$59 ==> null
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This bug is filed for clarification of specification (see comment)
Please clarify the specification to include a possible exception being thrown (ProviderException for RSASSA-PSS) or other possible exceptions for future Signature algorithms that require mandatory parameters by the user before any operations could be performed, and user did not set any parameters before using the Signature operations (sign, update, verify).
Or
null could be returned (as per specification)