Ambiguous method overloading for method

When i try to compile, it says: Ambiguous method overloading for method overloading for methode java.math.BigDecimal#
and it also says:
Cannot resolve which method to invoke for [null] due to overlapping prototypes between:…

def sql = ("Select d.*
from (select d.*,
             lead( (case when length <> 'N/A' then length else length_to_fault end)::float) over (partition by port_nbr, pair order by port, pair, d.add_date) as lengthh
      from diags d    
     ) d")

def lastRow = [id:-1, port_nbr:-1, pair:'', lengthh:-1.0]
dst_db1.eachRow( sql ) { row ->

  if ( row.port_nbr == lastRow.port_nbr && row.pair == lastRow.pair ) {
    BigDecimal lengthChange = 
      new BigDecimal( row.lengthh ) - new BigDecimal( lastRow.lengthh )

    if ( lengthChange > 30.0 ) {
        print "Port ${row.port_nbr}, ${row.pair} length change: $lengthChange"
        println "tbetween row ID ${lastRow.id} and ${row.id}"
    }
    lastRow = row
  } else {
    println "Key changed"
    lastRow = row
  }
}

can anyone try to fix this error?

EDIT- New full error:

Caught: java.lang.NumberFormatException: Character n is neither a decimal digit number, decimal point, nor "e" notation exponential mark.
java.lang.NumberFormatException: Character n is neither a decimal digit number, decimal point, nor "e" notation exponential mark.
        at java.base/jdk.internal.reflect.GeneratedConstructorAccessor10.newInstance(Unknown Source)
        at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at Main$_main_closure1.doCall(main.groovy:18)
        at jdk.internal.reflect.GeneratedMethodAccessor8.invoke(Unknown Source)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at Main.main(main.groovy:14)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

BigDecimal lengthChange = 
   new BigDecimal( "${row.lengthh}" ) - new BigDecimal( "${lastRow.lengthh}" )

println row.lengthh.class.name